Conditional handover (CHO) deconfiguration and failure handling in wireless communications

ABSTRACT

Methods, systems, and devices for wireless communications are described for management of conditional handover (CHO) configurations. A source base station may configure a user equipment (UE) with one or more CHO configurations for multiple target base stations. The CHO configurations may provide, for each target base station, one or more associated conditions that may trigger the UE to initiate a handover to the particular target base station, or to deconfigure a CHO configuration, such as based on a measurement threshold of one or more target base station measurements, one or more source base station measurements, or combinations thereof. The CHO configurations may also include failure handling information for initiating one or more subsequent handovers responsive to a failure of an initial handover attempt.

CROSS REFERENCE

The present Application for Patent claims the benefit of U.S.Provisional Patent Application No. 62/842,330 by PURKAYASTHA et al.,entitled “CONDITIONAL HANDOVER (CHO) DECONFIGURATION AND FAILUREHANDLING IN WIRELESS COMMUNICATIONS,” filed May 2, 2019, assigned to theassignee hereof, and expressly incorporated by reference herein.

BACKGROUND

The following relates generally to wireless communications, and morespecifically to conditional handover (CHO) deconfiguration and failurehandling in wireless communications.

Wireless communications systems are widely deployed to provide varioustypes of communication content such as voice, video, packet data,messaging, broadcast, and so on. These systems may be capable ofsupporting communication with multiple users by sharing the availablesystem resources (e.g., time, frequency, and power). Examples of suchmultiple-access systems include fourth generation (4G) systems such asLong Term Evolution (LTE) systems, LTE-Advanced (LTE-A) systems, orLTE-A Pro systems, and fifth generation (5G) systems which may bereferred to as New Radio (NR) systems. These systems may employtechnologies such as code division multiple access (CDMA), time divisionmultiple access (TDMA), frequency division multiple access (FDMA),orthogonal frequency division multiple access (OFDMA), or discreteFourier transform spread orthogonal frequency division multiplexing(DFT-S-OFDM). A wireless multiple-access communications system mayinclude a number of base stations or network access nodes, eachsimultaneously supporting communication for multiple communicationdevices, which may be otherwise known as user equipment (UE).

In some cases, a UE may be moving relative to one or more base stationswhich may result in the UE undergoing a handover procedure from a basestation that the UE is currently connected with (e.g., a source basestation) to a new base station (e.g., target base station). The handoverprocedure may be initiated by the source base station and target basestation exchanging information associated with the UE, and the sourcebase station sending a handover command to the UE. In some cases, the UEmay drop the connection with the source base station and initiate arandom access procedure with the target base station to establish aconnection with the target base station. In some cases, a one or morehandover configurations may be provided to a UE prior to the UEinitiating a handover, and the UE may initiate the handover upondetecting a condition that is indicated in the configuration, which maybe referred to as conditional handover (CHO). However, conditionalhandover configurations present challenges related to management of CHOconfigurations for target base stations.

SUMMARY

The described techniques relate to improved methods, systems, devices,and apparatuses that support conditional handover (CHO) deconfigurationand failure handling in wireless communications. Various aspects of thepresent disclosure describe techniques that provide for management ofCHO configurations. In some cases, a source base station may configure auser equipment (UE) with one or more CHO configurations for multipletarget base stations. The CHO configurations may provide, for eachtarget base station, one or more associated conditions that may triggerthe UE to initiate a handover to the particular target base station(e.g., based on a measurement threshold of one or more target basestation measurements, one or more source base station measurements, orcombinations thereof). In some cases, the CHO configurations may includefailure handling information, deconfiguration criteria, or combinationsthereof.

In some cases, the failure handling information may include one or moreCHO timer values, and upon transmitting a random access request to atarget base station, a UE may initiate a CHO timer associated with thetarget base station. In the event that the UE and target base stationare unable to complete the random access procedure prior to anexpiration of the CHO timer, the UE may identify that the handover tothe target base station has failed. In some cases, responsive to thefailure identification, the UE may determine whether any other targetbase stations have a CHO configuration, and may transmit a random accessrequest to a second target base station in the event that a CHOconfiguration is present for the second base station. The UE may repeatthe handover attempt and failure identification until the handover issuccessful or until no additional target base stations with CHOconfigurations are present, at which point the UE may declare a radiolink failure and initiate a connection re-establishment procedure.

In some cases, the one or more CHO configurations may includedeconfiguration criteria. In such cases, a UE may perform one or moremeasurements (e.g., signal strength or channel quality measurements) forthe source base station, one or more target base stations, orcombinations thereof. In cases where one or more of the measurements ofa particular target base station meet deconfiguration criteria, the UEmay deconfigure the CHO configuration associated with that particulartarget base station. In some cases, the UE may transmit a measurementreport to the source base station that may include the measurementassociated with the deconfigured target base station that the sourcebase station may use to release the handover configuration. In somecases, the UE may transmit a deconfiguration indication with themeasurement report (e.g., a cell ID of the target base station that isdeconfigured).

A method of wireless communication at a UE is described. The method mayinclude receiving, from a source base station, a conditional handoverconfiguration that indicates one or more target base stations, one ormore measurement thresholds for initiating a handover from the sourcebase station to the one or more target base stations, and one or moretimers associated with the handover to the one or more target basestations, determining, based on the conditional handover configuration,that a first measurement threshold for initiating the handover to afirst target base station is satisfied, transmitting, based on theconditional handover configuration, a first random access request to thefirst target base station to initiate a first random access procedurefor the handover to the first target base station, starting a firstconditional handover timer for completing the first random accessprocedure responsive to the transmitting the first random accessrequest, and determining a first conditional handover failure responsiveto the first conditional handover timer expiring prior to completing thefirst random access procedure.

An apparatus for wireless communication at a UE is described. Theapparatus may include a processor, memory in electronic communicationwith the processor, and instructions stored in the memory. Theinstructions may be executable by the processor to cause the apparatusto receive, from a source base station, a conditional handoverconfiguration that indicates one or more target base stations, one ormore measurement thresholds for initiating a handover from the sourcebase station to the one or more target base stations, and one or moretimers associated with the handover to the one or more target basestations, determine, based on the conditional handover configuration,that a first measurement threshold for initiating the handover to afirst target base station is satisfied, transmit, based on theconditional handover configuration, a first random access request to thefirst target base station to initiate a first random access procedurefor the handover to the first target base station, start a firstconditional handover timer for completing the first random accessprocedure responsive to the transmitting the first random accessrequest, and determine a first conditional handover failure responsiveto the first conditional handover timer expiring prior to completing thefirst random access procedure.

Another apparatus for wireless communication at a UE is described. Theapparatus may include means for receiving, from a source base station, aconditional handover configuration that indicates one or more targetbase stations, one or more measurement thresholds for initiating ahandover from the source base station to the one or more target basestations, and one or more timers associated with the handover to the oneor more target base stations, determining, based on the conditionalhandover configuration, that a first measurement threshold forinitiating the handover to a first target base station is satisfied,transmitting, based on the conditional handover configuration, a firstrandom access request to the first target base station to initiate afirst random access procedure for the handover to the first target basestation, starting a first conditional handover timer for completing thefirst random access procedure responsive to the transmitting the firstrandom access request, and determining a first conditional handoverfailure responsive to the first conditional handover timer expiringprior to completing the first random access procedure.

A non-transitory computer-readable medium storing code for wirelesscommunication at a UE is described. The code may include instructionsexecutable by a processor to receive, from a source base station, aconditional handover configuration that indicates one or more targetbase stations, one or more measurement thresholds for initiating ahandover from the source base station to the one or more target basestations, and one or more timers associated with the handover to the oneor more target base stations, determine, based on the conditionalhandover configuration, that a first measurement threshold forinitiating the handover to a first target base station is satisfied,transmit, based on the conditional handover configuration, a firstrandom access request to the first target base station to initiate afirst random access procedure for the handover to the first target basestation, start a first conditional handover timer for completing thefirst random access procedure responsive to the transmitting the firstrandom access request, and determine a first conditional handoverfailure responsive to the first conditional handover timer expiringprior to completing the first random access procedure.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, the one or more timersinclude at least the first conditional handover timer for completing thefirst random access procedure with the first target base station. Insome examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, the conditional handoverconfiguration includes at least a first conditional handoverconfiguration for the first target base station and a second conditionalhandover configuration for a second target base station.

Some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein may further includeoperations, features, means, or instructions for determining, responsiveto the first conditional handover timer expiring, that a secondmeasurement threshold for initiating a handover to a second target basestation is satisfied, transmitting, based on the conditional handoverconfiguration, a second random access request to the second target basestation to initiate a second random access procedure for the handover tothe second target base station, starting a second conditional handovertimer for completing the second random access procedure, and repeatingthe determining, transmitting, and starting for any other target basestations configured for conditional handover upon further conditionalhandover failures. Some examples of the method, apparatuses, andnon-transitory computer-readable medium described herein may furtherinclude operations, features, means, or instructions for initiating aconnection re-establishment procedure upon determining that no othertarget base stations are configured for conditional handover.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, a first duration of the firstconditional handover timer may be different than a second duration ofthe second conditional handover timer. Some examples of the method,apparatuses, and non-transitory computer-readable medium describedherein may further include operations, features, means, or instructionsfor selecting, responsive to the first conditional handover timerexpiring, the second target base station from a set of available targetbase stations based on one or more of a channel quality measurementassociated with each of the set of available target base stations, orany combinations thereof.

Some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein may further includeoperations, features, means, or instructions for receiving, from thesource base station, a deconfiguration message that deconfigures one ormore conditional handover configurations, and deconfiguring the one ormore conditional handover configurations based at least in part on thedeconfiguration message. In some examples of the method, apparatuses,and non-transitory computer-readable medium described herein, thedeconfiguration message is received in radio resource control signalingfrom the source base station. Some examples of the method, apparatuses,and non-transitory computer-readable medium described herein may furtherinclude operations, features, means, or instructions for deleting one ormore of a radio resource control configuration or a first measurementand reporting configuration for conditional handover trigger provided ina first conditional handover configuration, and discontinuingconditional handover measurements associated with the conditionalhandover configuration and evaluation of whether the measurements meetconditional handover criteria.

A method of wireless communication at a UE is described. The method mayinclude receiving, from a source base station, a conditional handoverconfiguration that indicates one or more conditional handoverconfigurations associated with one or more target base stations, whereeach of the one or more conditional handover configurations include atriggering measurement threshold for initiating a conditional handoverto an associated target base station and a deconfiguration measurementthreshold for deconfiguring the conditional handover configuration ofthe associated target base station, determining, based on theconditional handover configuration, that a first deconfigurationmeasurement threshold for deconfiguring a first conditional handoverconfiguration of a first target base station is satisfied, and releasingthe first conditional handover configuration of the first target basestation.

An apparatus for wireless communication at a UE is described. Theapparatus may include a processor, memory in electronic communicationwith the processor, and instructions stored in the memory. Theinstructions may be executable by the processor to cause the apparatusto receive, from a source base station, a conditional handoverconfiguration that indicates one or more conditional handoverconfigurations associated with one or more target base stations, whereeach of the one or more conditional handover configurations include atriggering measurement threshold for initiating a conditional handoverto an associated target base station and a deconfiguration measurementthreshold for deconfiguring the conditional handover configuration ofthe associated target base station, determine, based on the conditionalhandover configuration, that a first deconfiguration measurementthreshold for deconfiguring a first conditional handover configurationof a first target base station is satisfied, and release the firstconditional handover configuration of the first target base station.

Another apparatus for wireless communication at a UE is described. Theapparatus may include means for receiving, from a source base station, aconditional handover configuration that indicates one or moreconditional handover configurations associated with one or more targetbase stations, where each of the one or more conditional handoverconfigurations include a triggering measurement threshold for initiatinga conditional handover to an associated target base station and adeconfiguration measurement threshold for deconfiguring the conditionalhandover configuration of the associated target base station,determining, based on the conditional handover configuration, that afirst deconfiguration measurement threshold for deconfiguring a firstconditional handover configuration of a first target base station issatisfied, and releasing the first conditional handover configuration ofthe first target base station.

A non-transitory computer-readable medium storing code for wirelesscommunication at a UE is described. The code may include instructionsexecutable by a processor to receive, from a source base station, aconditional handover configuration that indicates one or moreconditional handover configurations associated with one or more targetbase stations, where each of the one or more conditional handoverconfigurations include a triggering measurement threshold for initiatinga conditional handover to an associated target base station and adeconfiguration measurement threshold for deconfiguring the conditionalhandover configuration of the associated target base station, determine,based on the conditional handover configuration, that a firstdeconfiguration measurement threshold for deconfiguring a firstconditional handover configuration of a first target base station issatisfied, and release the first conditional handover configuration ofthe first target base station.

Some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein may further includeoperations, features, means, or instructions for determining, based onthe conditional handover configuration, that a second triggeringmeasurement threshold for initiating a handover to a second target basestation is satisfied, and transmitting, based on a second conditionalhandover configuration of the second target base station, a randomaccess request to the second target base station to initiate a randomaccess procedure for the handover to the second target base station.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, the releasing the firstconditional handover configuration may include operations, features,means, or instructions for deleting one or more of a radio resourcecontrol configuration, a first measurement and reporting configurationfor conditional handover trigger and conditional handoverdeconfiguration trigger, or one or more timers associated with the firsttarget base station, that are provided in the first conditional handoverconfiguration, and discontinuing conditional handover measurementsassociated with the first target base station and evaluations of whetherthe measurements meet conditional handover criteria or conditionalhandover deconfiguration criteria.

Some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein may further includeoperations, features, means, or instructions for transmitting ameasurement report to the source base station that indicates the firstconditional handover configuration of the first target base station arereleased. In some examples of the method, apparatuses, andnon-transitory computer-readable medium described herein, themeasurement report contains a deconfiguration indication for the firsttarget base station.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, the first deconfigurationmeasurement threshold may be a channel quality threshold associated withthe first target base station, and where the first conditional handoverconfiguration is released responsive to a channel quality measurement ofthe first target base station being below the channel quality threshold.In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, the first deconfigurationmeasurement threshold includes a first threshold value associated withthe source base station and a second threshold value associated with thefirst target base station, and where the first conditional handoverconfiguration is released responsive to a first channel qualitymeasurement of the source base station exceeding the first threshold anda second channel quality measurement of the first target base stationbeing below the second threshold value. In some examples of the method,apparatuses, and non-transitory computer-readable medium describedherein, the first deconfiguration measurement threshold may be adifference threshold, and where the first conditional handoverconfiguration is released responsive to a difference between channelquality measurements of the source base station and the first targetbase station exceeding the difference threshold.

A method of wireless communication at a source base station isdescribed. The method may include establishing, by the source basestation, one or more conditional handover configurations with one ormore target base stations for a conditional handover of a UE from thesource base station to the respective target base station, where eachconditional handover configuration includes a conditional handover timeperiod for completing a random access procedure upon initiation of theconditional handover of the UE from the source base station to therespective target base station and transmitting, to the UE, the one ormore conditional handover configurations that each indicate anassociated target base station, one or more measurement thresholds forinitiating the handover of the UE from the source base station to theassociated target base station, and the conditional handover time periodof the associated target base station.

An apparatus for wireless communication at a source base station isdescribed. The apparatus may include a processor, memory in electroniccommunication with the processor, and instructions stored in the memory.The instructions may be executable by the processor to cause theapparatus to establish, by the source base station, one or moreconditional handover configurations with one or more target basestations for a conditional handover of a UE from the source base stationto the respective target base station, where each conditional handoverconfiguration includes a conditional handover time period for completinga random access procedure upon initiation of the conditional handover ofthe UE from the source base station to the respective target basestation and transmit, to the UE, the one or more conditional handoverconfigurations that each indicate an associated target base station, oneor more measurement thresholds for initiating the handover of the UEfrom the source base station to the associated target base station, andthe conditional handover time period of the associated target basestation.

Another apparatus for wireless communication at a source base station isdescribed. The apparatus may include means for establishing, by thesource base station, one or more conditional handover configurationswith one or more target base stations for a conditional handover of a UEfrom the source base station to the respective target base station,where each conditional handover configuration includes a conditionalhandover time period for completing a random access procedure uponinitiation of the conditional handover of the UE from the source basestation to the respective target base station and transmitting, to theUE, the one or more conditional handover configurations that eachindicate an associated target base station, one or more measurementthresholds for initiating the handover of the UE from the source basestation to the associated target base station, and the conditionalhandover time period of the associated target base station.

A non-transitory computer-readable medium storing code for wirelesscommunication at a source base station is described. The code mayinclude instructions executable by a processor to establish, by thesource base station, one or more conditional handover configurationswith one or more target base stations for a conditional handover of a UEfrom the source base station to the respective target base station,where each conditional handover configuration includes a conditionalhandover time period for completing a random access procedure uponinitiation of the conditional handover of the UE from the source basestation to the respective target base station and transmit, to the UE,the one or more conditional handover configurations that each indicatean associated target base station, one or more measurement thresholdsfor initiating the handover of the UE from the source base station tothe associated target base station, and the conditional handover timeperiod of the associated target base station.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, each of the one or moretarget base stations may have a different value for the conditionalhandover time period. In some examples of the method, apparatuses, andnon-transitory computer-readable medium described herein, theconditional handover time period may be determined based on one or moreof an estimate of movement of the UE relative to each respective targetbase station, a traffic load of the source base station or eachrespective target base station, channel quality measurements for eachrespective target base station provided by the UE, or any combinationsthereof.

A method of wireless communication at a source base station isdescribed. The method may include establishing, by the source basestation, one or more conditional handover configurations with one ormore target base stations for a conditional handover of a UE from thesource base station to the respective target base station, where eachconditional handover configuration includes a triggering measurementthreshold for initiating the conditional handover of the UE to anassociated target base station, a conditional handover timer value forcompleting the conditional handover of the UE to the associated targetbase station, and a deconfiguration measurement threshold fordeconfiguring the conditional handover configuration of the associatedtarget base station, and transmitting, to the UE, the one or moreconditional handover configurations that each indicate the associatedtarget base station, the triggering measurement threshold for initiatingthe conditional handover to the associated target base station, theconditional handover timer value for completing the conditional handoverof the UE to the associated target base station, and the deconfigurationmeasurement threshold for deconfiguring the conditional handoverconfiguration of the associated target base station.

An apparatus for wireless communication at a source base station isdescribed. The apparatus may include a processor, memory in electroniccommunication with the processor, and instructions stored in the memory.The instructions may be executable by the processor to cause theapparatus to establish, by the source base station, one or moreconditional handover configurations with one or more target basestations for a conditional handover of a UE from the source base stationto the respective target base station, where each conditional handoverconfiguration includes a triggering measurement threshold for initiatingthe conditional handover of the UE to an associated target base station,a conditional handover timer value for completing the conditionalhandover of the UE to the associated target base station, and adeconfiguration measurement threshold for deconfiguring the conditionalhandover configuration of the associated target base station, andtransmit, to the UE, the one or more conditional handover configurationsthat each indicate the associated target base station, the triggeringmeasurement threshold for initiating the conditional handover to theassociated target base station, the conditional handover timer value forcompleting the conditional handover of the UE to the associated targetbase station, and the deconfiguration measurement threshold fordeconfiguring the conditional handover configuration of the associatedtarget base station.

Another apparatus for wireless communication at a source base station isdescribed. The apparatus may include means for establishing, by thesource base station, one or more conditional handover configurationswith one or more target base stations for a conditional handover of a UEfrom the source base station to the respective target base station,where each conditional handover configuration includes a triggeringmeasurement threshold for initiating the conditional handover of the UEto an associated target base station, a conditional handover timer valuefor completing the conditional handover of the UE to the associatedtarget base station, and a deconfiguration measurement threshold fordeconfiguring the conditional handover configuration of the associatedtarget base station, and transmitting, to the UE, the one or moreconditional handover configurations that each indicate the associatedtarget base station, the triggering measurement threshold for initiatingthe conditional handover to the associated target base station, theconditional handover timer value for completing the conditional handoverof the UE to the associated target base station, and the deconfigurationmeasurement threshold for deconfiguring the conditional handoverconfiguration of the associated target base station.

A non-transitory computer-readable medium storing code for wirelesscommunication at a source base station is described. The code mayinclude instructions executable by a processor to establish, by thesource base station, one or more conditional handover configurationswith one or more target base stations for a conditional handover of a UEfrom the source base station to the respective target base station,where each conditional handover configuration includes a triggeringmeasurement threshold for initiating the conditional handover of the UEto an associated target base station, a conditional handover timer valuefor completing the conditional handover of the UE to the associatedtarget base station, and a deconfiguration measurement threshold fordeconfiguring the conditional handover configuration of the associatedtarget base station, and transmit, to the UE, the one or moreconditional handover configurations that each indicate the associatedtarget base station, the triggering measurement threshold for initiatingthe conditional handover to the associated target base station, theconditional handover timer value for completing the conditional handoverof the UE to the associated target base station, and the deconfigurationmeasurement threshold for deconfiguring the conditional handoverconfiguration of the associated target base station.

Some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein may further includeoperations, features, means, or instructions for determining todeconfigure at least one a first conditional handover configuration atthe UE, transmitting, responsive to the determining to deconfigure,deconfiguration information to the UE that indicates the UE is to deleteone or more of a radio resource control configuration or a firstmeasurement and reporting configuration for the first conditionalhandover configuration, and releasing the first conditional handoverconfiguration of the first target base station.

Some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein may further includeoperations, features, means, or instructions for receiving, from the UE,a measurement report that indicates that a first deconfigurationmeasurement threshold for deconfiguring a first conditional handoverconfiguration of a first target base station is satisfied, and releasingthe first conditional handover configuration of the first target basestation responsive to the measurement report. In some examples of themethod, apparatuses, and non-transitory computer-readable mediumdescribed herein, the releasing the first conditional handoverconfiguration may include operations, features, means, or instructionsfor deleting one or more of a radio resource control configuration, thefirst deconfiguration measurement threshold, a first triggeringmeasurement threshold, or one or more timers associated with the firsttarget base station, that are included in the first conditional handoverconfiguration.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, the releasing the firstconditional handover configuration further may include operations,features, means, or instructions for providing an indication to thefirst target base station that the first conditional handoverconfiguration is released.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, the deconfigurationmeasurement threshold may be a channel quality threshold associated witheach respective target base station, and where the conditional handoverconfiguration of a first target base station is released responsive to achannel quality measurement of the first target base station being belowthe channel quality threshold of the first target base station. In someexamples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, the deconfigurationmeasurement threshold includes a first threshold value associated withthe source base station and a second threshold value for each respectivetarget base station, and where the conditional handover configuration ofa first target base station is released responsive to a first channelquality measurement of the source base station exceeding the firstthreshold and a second channel quality measurement of the first targetbase station being below the second threshold value of the first targetbase station. In some examples of the method, apparatuses, andnon-transitory computer-readable medium described herein, thedeconfiguration measurement threshold may be a difference threshold, andwhere the conditional handover configuration associated with a firsttarget base station is released responsive to a difference betweenchannel quality measurements of the source base station and the firsttarget base station exceeding the difference threshold.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a system for wireless communicationsthat supports conditional handover (CHO) deconfiguration and failurehandling in wireless communications in accordance with aspects of thepresent disclosure.

FIG. 2 illustrates an example of a portion of a wireless communicationssystem with source and target base stations that supports CHOdeconfiguration and failure handling in wireless communications inaccordance with aspects of the present disclosure.

FIGS. 3 through 7 illustrate example process flows that support CHOdeconfiguration and failure handling in wireless communications inaccordance with aspects of the present disclosure.

FIGS. 8 and 9 show block diagrams of devices that support CHOdeconfiguration and failure handling in wireless communications inaccordance with aspects of the present disclosure.

FIG. 10 shows a block diagram of a communications manager that supportsCHO deconfiguration and failure handling in wireless communications inaccordance with aspects of the present disclosure.

FIG. 11 shows a diagram of a system including a device that supports CHOdeconfiguration and failure handling in wireless communications inaccordance with aspects of the present disclosure.

FIGS. 12 and 13 show block diagrams of devices that support CHOdeconfiguration and failure handling in wireless communications inaccordance with aspects of the present disclosure.

FIG. 14 shows a block diagram of a communications manager that supportsCHO deconfiguration and failure handling in wireless communications inaccordance with aspects of the present disclosure.

FIG. 15 shows a diagram of a system including a device that supports CHOdeconfiguration and failure handling in wireless communications inaccordance with aspects of the present disclosure.

FIGS. 16 through 22 show flowcharts illustrating methods that supportCHO deconfiguration and failure handling in wireless communications inaccordance with aspects of the present disclosure.

DETAILED DESCRIPTION

Various aspects of the present disclosure provide techniques for userequipment (UE) handover in a wireless communications system. A UE mayundergo a handover procedure from a source cell to a target cell inwhich the UE may release or drop an existing connection with the sourcecell to establish a new connection with the target cell. The handoverprocedure may be initiated by the source base station and target basestation exchanging information associated with the UE, and the sourcebase station sending a handover command to the UE. In some cases, the UEmay drop the existing connection with the source base station uponreceiving the handover command, and initiate a random access procedurewith the target base station to establish a connection with the targetbase station. In some cases, a one or more handover configurations maybe provided to a UE prior to the UE initiating a handover, and the UEmay initiate the handover upon detecting a condition that is indicatedin the configuration, which may be referred to as conditional handover(CHO).

In some aspects of the present disclosure, a source base station mayconfigure a UE with one or more CHO configurations for multiple targetbase stations. The CHO configurations may provide, for each target basestation, one or more associated conditions that may trigger the UE toinitiate a handover to the particular target base station (e.g., basedon a measurement threshold of one or more target base stationmeasurements, one or more source base station measurements, orcombinations thereof), and one or more associated conditions todeconfigure the CHO configuration. In some cases, the CHO configurationsmay include failure handling information, deconfiguration criteria, orcombinations thereof.

In some cases, CHO configurations may provide one or more handovercriteria for one or more target base stations. The UE may perform one ormore measurements of the target base station(s), the source basestation, or combinations thereof, and if the measurements meet thehandover criteria the UE may initiate the handover with a target basestation that met the handover criteria (e.g., by transmitting a randomaccess request to the target base station). While CHO configurations mayallow for a UE to autonomously initiate a handover in the event thathandover criteria are met (e.g., if a source base station measurement isbelow a threshold and the target base station measurement is above athreshold), maintaining such configurations may consume resources at thebase stations and UE, constrain flexibility of one or more target basestations, consume overhead associated with target base stationmeasurements, and the like.

For example, a source base station may configure a CHO with a firsttarget base station, which may result in the source base stationperiodically providing the first target base station with informationassociated with the UE, the first target base station reserving acontention-free random access preamble for the UE (which may constrainthe first target base station from allocating contention-free preamblesto other devices), the UE performing measurements on the first targetbase station, the UE transmitting measurement reports with the firsttarget base station measurements, and the like. Accordingly, in theevent that the first target base station is no longer a suitablecandidate for handover of the UE, deconfiguring the CHO of the firsttarget base station may be beneficial to the UE, the source basestation, and the target base station. Further, if the random accessprocedure that is initiated as part of a CHO is unsuccessful or there isa radio link failure, service interruption or latency may be increased.

In accordance with various techniques discussed herein, in some casesone or more CHO configurations may include deconfiguration criteria. Insuch cases, a UE may perform one or more measurements (e.g., signalstrength or channel quality measurements) for the source base station,one or more target base stations, or combinations thereof. In caseswhere one or more of the measurements of a first target base stationmeet deconfiguration criteria, the UE may deconfigure the CHOconfiguration associated with the first target base station. In somecases, the UE may autonomously deconfigure the CHO configuration. Insome cases, the UE may transmit a measurement report to the source basestation that may include the measurement associated with thedeconfigured first target base station that the source base station mayuse to release the handover configuration. In some cases, the UE maytransmit a deconfiguration indication with the measurement report (e.g.,a cell ID of the target base station that is deconfigured). In othercases, the UE may maintain the CHO configuration until the source basestation transmits a deconfiguration to the UE responsive to themeasurement report. The source base station may also provide acancellation indication to the first target base station, which mayallow the first target base station to release resources reserved forthe UE

Additionally or alternatively, in some cases CHO configurations mayinclude one or more CHO timer values, and upon transmitting a randomaccess request to a target base station, a UE may initiate a CHO timerassociated with the target base station. In the event that the UE andtarget base station are unable to complete the random access procedureprior to an expiration of the CHO timer, the UE may identify that thehandover to the target base station has failed. In some cases,responsive to the failure identification, the UE may determine whetherany other target base stations have a CHO configuration, and maytransmit a random access request to a second target base station in theevent that a CHO configuration is present for the second base station.The UE may repeat the handover attempt and failure identification untilthe handover is successful or until no additional target base stationswith CHO configurations are present, at which point the UE may declare aradio link failure and initiate a connection re-establishment procedure.

Such techniques may allow for efficient management of CHO configurationsand failure handling for failed CHO handovers. Deconfiguration of CHOconfigurations may allow for more efficient management of CHOconfigurations by deconfiguring CHO configurations based on measurementsof a UE, which may allow for a relatively current set of CHOconfigurations that may be reliably used for handovers in the event thathandover criteria are met. Further, failure handling techniquesdiscussed herein may reduce latency and service interruptions associatedwith a failed random access procedure of a handover attempt.

Aspects of the disclosure are initially described in the context of awireless communications system. Various exemplary process flows are thendiscussed that describe CHO configuration management and failurehandling. Aspects of the disclosure are further illustrated by anddescribed with reference to apparatus diagrams, system diagrams, andflowcharts that relate to CHO deconfiguration and failure handling inwireless communications.

FIG. 1 illustrates an example of a wireless communications system 100that supports CHO deconfiguration and failure handling in wirelesscommunications in accordance with aspects of the present disclosure. Thewireless communications system 100 includes base stations 105, UEs 115,and a core network 130. In some examples, the wireless communicationssystem 100 may be a Long Term Evolution (LTE) network, an LTE-Advanced(LTE-A) network, an LTE-A Pro network, or a New Radio (NR) network. Insome cases, wireless communications system 100 may support enhancedbroadband communications, ultra-reliable (e.g., mission critical)communications, low latency communications, or communications withlow-cost and low-complexity devices.

Base stations 105 may wirelessly communicate with UEs 115 via one ormore base station antennas. Base stations 105 described herein mayinclude or may be referred to by those skilled in the art as a basetransceiver station, a radio base station, an access point, a radiotransceiver, a NodeB, an eNodeB (eNB), a next-generation NodeB orgiga-NodeB (either of which may be referred to as a gNB), a Home NodeB,a Home eNodeB, or some other suitable terminology. Wirelesscommunications system 100 may include base stations 105 of differenttypes (e.g., macro or small cell base stations). The UEs 115 describedherein may be able to communicate with various types of base stations105 and network equipment including macro eNBs, small cell eNBs, gNBs,relay base stations, and the like.

Each base station 105 may be associated with a particular geographiccoverage area 110 in which communications with various UEs 115 issupported. Each base station 105 may provide communication coverage fora respective geographic coverage area 110 via communication links 125,and communication links 125 between a base station 105 and a UE 115 mayutilize one or more carriers. Communication links 125 shown in wirelesscommunications system 100 may include uplink transmissions from a UE 115to a base station 105, or downlink transmissions from a base station 105to a UE 115. Downlink transmissions may also be called forward linktransmissions while uplink transmissions may also be called reverse linktransmissions.

The geographic coverage area 110 for a base station 105 may be dividedinto sectors making up a portion of the geographic coverage area 110,and each sector may be associated with a cell. For example, each basestation 105 may provide communication coverage for a macro cell, a smallcell, a hot spot, or other types of cells, or various combinationsthereof. In some examples, a base station 105 may be movable andtherefore provide communication coverage for a moving geographiccoverage area 110. In some examples, different geographic coverage areas110 associated with different technologies may overlap, and overlappinggeographic coverage areas 110 associated with different technologies maybe supported by the same base station 105 or by different base stations105. The wireless communications system 100 may include, for example, aheterogeneous LTE/LTE-A/LTE-A Pro or NR network in which different typesof base stations 105 provide coverage for various geographic coverageareas 110.

The term “cell” refers to a logical communication entity used forcommunication with a base station 105 (e.g., over a carrier), and may beassociated with an identifier for distinguishing neighboring cells(e.g., a physical cell identifier (PCID), a virtual cell identifier(VCID)) operating via the same or a different carrier. In some examples,a carrier may support multiple cells, and different cells may beconfigured according to different protocol types (e.g., machine-typecommunication (MTC), narrowband Internet-of-Things (NB-IoT), enhancedmobile broadband (eMBB), or others) that may provide access fordifferent types of devices. In some cases, the term “cell” may refer toa portion of a geographic coverage area 110 (e.g., a sector) over whichthe logical entity operates.

UEs 115 may be dispersed throughout the wireless communications system100, and each UE 115 may be stationary or mobile. A UE 115 may also bereferred to as a mobile device, a wireless device, a remote device, ahandheld device, or a subscriber device, or some other suitableterminology, where the “device” may also be referred to as a unit, astation, a terminal, or a client. A UE 115 may also be a personalelectronic device such as a cellular phone, a personal digital assistant(PDA), a tablet computer, a laptop computer, or a personal computer. Insome examples, a UE 115 may also refer to a wireless local loop (WLL)station, an Internet of Things (IoT) device, an Internet of Everything(IoE) device, or an MTC device, or the like, which may be implemented invarious articles such as appliances, vehicles, meters, or the like.

Some UEs 115, such as MTC or IoT devices, may be low cost or lowcomplexity devices, and may provide for automated communication betweenmachines (e.g., via Machine-to-Machine (M2M) communication). M2Mcommunication or MTC may refer to data communication technologies thatallow devices to communicate with one another or a base station 105without human intervention. In some examples, M2M communication or MTCmay include communications from devices that integrate sensors or metersto measure or capture information and relay that information to acentral server or application program that can make use of theinformation or present the information to humans interacting with theprogram or application. Some UEs 115 may be designed to collectinformation or enable automated behavior of machines. Examples ofapplications for MTC devices include smart metering, inventorymonitoring, water level monitoring, equipment monitoring, healthcaremonitoring, wildlife monitoring, weather and geological eventmonitoring, fleet management and tracking, remote security sensing,physical access control, and transaction-based business charging.

Some UEs 115 may be configured to employ operating modes that reducepower consumption, such as half-duplex communications (e.g., a mode thatsupports one-way communication via transmission or reception, but nottransmission and reception simultaneously). In some examples half-duplexcommunications may be performed at a reduced peak rate. Other powerconservation techniques for UEs 115 include entering a power saving“deep sleep” mode when not engaging in active communications, oroperating over a limited bandwidth (e.g., according to narrowbandcommunications). In some cases, UEs 115 may be designed to supportcritical functions (e.g., mission critical functions), and a wirelesscommunications system 100 may be configured to provide ultra-reliablecommunications for these functions.

In some cases, a UE 115 may also be able to communicate directly withother UEs 115 (e.g., using a peer-to-peer (P2P) or device-to-device(D2D) protocol). One or more of a group of UEs 115 utilizing D2Dcommunications may be within the geographic coverage area 110 of a basestation 105. Other UEs 115 in such a group may be outside the geographiccoverage area 110 of a base station 105, or be otherwise unable toreceive transmissions from a base station 105. In some cases, groups ofUEs 115 communicating via D2D communications may utilize a one-to-many(1:M) system in which each UE 115 transmits to every other UE 115 in thegroup. In some cases, a base station 105 facilitates the scheduling ofresources for D2D communications. In other cases, D2D communications arecarried out between UEs 115 without the involvement of a base station105.

Base stations 105 may communicate with the core network 130 and with oneanother. For example, base stations 105 may interface with the corenetwork 130 through backhaul links 132 (e.g., via an S1, N2, N3, orother interface). Base stations 105 may communicate with one anotherover backhaul links 134 (e.g., via an X2, Xn, or other interface) eitherdirectly (e.g., directly between base stations 105) or indirectly (e.g.,via core network 130).

The core network 130 may provide user authentication, accessauthorization, tracking, Internet Protocol (IP) connectivity, and otheraccess, routing, or mobility functions. The core network 130 may be anevolved packet core (EPC), which may include at least one mobilitymanagement entity (MME), at least one serving gateway (S-GW), and atleast one Packet Data Network (PDN) gateway (P-GW). The MME may managenon-access stratum (e.g., control plane) functions such as mobility,authentication, and bearer management for UEs 115 served by basestations 105 associated with the EPC. User IP packets may be transferredthrough the S-GW, which itself may be connected to the P-GW. The P-GWmay provide IP address allocation as well as other functions. The P-GWmay be connected to the network operators IP services. The operators IPservices may include access to the Internet, Intranet(s), an IPMultimedia Subsystem (IMS), or a Packet-Switched (PS) Streaming Service.

At least some of the network devices, such as a base station 105, mayinclude subcomponents such as an access network entity, which may be anexample of an access node controller (ANC). Each access network entitymay communicate with UEs 115 through a number of other access networktransmission entities, which may be referred to as a radio head, a smartradio head, or a transmission/reception point (TRP). In someconfigurations, various functions of each access network entity or basestation 105 may be distributed across various network devices (e.g.,radio heads and access network controllers) or consolidated into asingle network device (e.g., a base station 105).

Wireless communications system 100 may operate using one or morefrequency bands, typically in the range of 300 megahertz (MHz) to 300gigahertz (GHz). Generally, the region from 300 MHz to 3 GHz is known asthe ultra-high frequency (UHF) region or decimeter band, since thewavelengths range from approximately one decimeter to one meter inlength. UHF waves may be blocked or redirected by buildings andenvironmental features. However, the waves may penetrate structuressufficiently for a macro cell to provide service to UEs 115 locatedindoors. Transmission of UHF waves may be associated with smallerantennas and shorter range (e.g., less than 100 km) compared totransmission using the smaller frequencies and longer waves of the highfrequency (HF) or very high frequency (VHF) portion of the spectrumbelow 300 MHz.

Wireless communications system 100 may also operate in a super highfrequency (SHF) region using frequency bands from 3 GHz to 30 GHz, alsoknown as the centimeter band. The SHF region includes bands such as the5 GHz industrial, scientific, and medical (ISM) bands, which may be usedopportunistically by devices that may be capable of toleratinginterference from other users.

Wireless communications system 100 may also operate in an extremely highfrequency (EHF) region of the spectrum (e.g., from 30 GHz to 300 GHz),also known as the millimeter band. In some examples, wirelesscommunications system 100 may support millimeter wave (mmW)communications between UEs 115 and base stations 105, and EHF antennasof the respective devices may be even smaller and more closely spacedthan UHF antennas. In some cases, this may facilitate use of antennaarrays within a UE 115. However, the propagation of EHF transmissionsmay be subject to even greater atmospheric attenuation and shorter rangethan SHF or UHF transmissions. Techniques disclosed herein may beemployed across transmissions that use one or more different frequencyregions, and designated use of bands across these frequency regions maydiffer by country or regulating body.

In some cases, wireless communications system 100 may utilize bothlicensed and unlicensed radio frequency spectrum bands. For example,wireless communications system 100 may employ License Assisted Access(LAA), LTE-Unlicensed (LTE-U) radio access technology, or NR technologyin an unlicensed band such as the 5 GHz ISM band. When operating inunlicensed radio frequency spectrum bands, wireless devices such as basestations 105 and UEs 115 may employ listen-before-talk (LBT) proceduresto ensure a frequency channel is clear before transmitting data. In somecases, operations in unlicensed bands may be based on a carrieraggregation configuration in conjunction with component carriersoperating in a licensed band (e.g., LAA). Operations in unlicensedspectrum may include downlink transmissions, uplink transmissions,peer-to-peer transmissions, or a combination of these. Duplexing inunlicensed spectrum may be based on frequency division duplexing (FDD),time division duplexing (TDD), or a combination of both.

In some examples, base station 105 or UE 115 may be equipped withmultiple antennas, which may be used to employ techniques such astransmit diversity, receive diversity, multiple-input multiple-output(MIMO) communications, or beamforming. For example, wirelesscommunications system 100 may use a transmission scheme between atransmitting device (e.g., a base station 105) and a receiving device(e.g., a UE 115), where the transmitting device is equipped withmultiple antennas and the receiving device is equipped with one or moreantennas. MIMO communications may employ multipath signal propagation toincrease the spectral efficiency by transmitting or receiving multiplesignals via different spatial layers, which may be referred to asspatial multiplexing. The multiple signals may, for example, betransmitted by the transmitting device via different antennas ordifferent combinations of antennas. Likewise, the multiple signals maybe received by the receiving device via different antennas or differentcombinations of antennas. Each of the multiple signals may be referredto as a separate spatial stream, and may carry bits associated with thesame data stream (e.g., the same codeword) or different data streams.Different spatial layers may be associated with different antenna portsused for channel measurement and reporting. MIMO techniques includesingle-user MIMO (SU-MIMO) where multiple spatial layers are transmittedto the same receiving device, and multiple-user MIMO (MU-MIMO) wheremultiple spatial layers are transmitted to multiple devices.

Beamforming, which may also be referred to as spatial filtering,directional transmission, or directional reception, is a signalprocessing technique that may be used at a transmitting device or areceiving device (e.g., a base station 105 or a UE 115) to shape orsteer an antenna beam (e.g., a transmit beam or receive beam) along aspatial path between the transmitting device and the receiving device.Beamforming may be achieved by combining the signals communicated viaantenna elements of an antenna array such that signals propagating atparticular orientations with respect to an antenna array experienceconstructive interference while others experience destructiveinterference. The adjustment of signals communicated via the antennaelements may include a transmitting device or a receiving deviceapplying certain amplitude and phase offsets to signals carried via eachof the antenna elements associated with the device. The adjustmentsassociated with each of the antenna elements may be defined by abeamforming weight set associated with a particular orientation (e.g.,with respect to the antenna array of the transmitting device orreceiving device, or with respect to some other orientation).

In one example, a base station 105 may use multiple antennas or antennaarrays to conduct beamforming operations for directional communicationswith a UE 115. For instance, some signals (e.g. synchronization signals,reference signals, beam selection signals, or other control signals) maybe transmitted by a base station 105 multiple times in differentdirections, which may include a signal being transmitted according todifferent beamforming weight sets associated with different directionsof transmission. Transmissions in different beam directions may be usedto identify (e.g., by the base station 105 or a receiving device, suchas a UE 115) a beam direction for subsequent transmission and/orreception by the base station 105.

In some cases, the antennas of a base station 105 or UE 115 may belocated within one or more antenna arrays, which may support MIMOoperations, or transmit or receive beamforming. For example, one or morebase station antennas or antenna arrays may be co-located at an antennaassembly, such as an antenna tower. In some cases, antennas or antennaarrays associated with a base station 105 may be located in diversegeographic locations. A base station 105 may have an antenna array witha number of rows and columns of antenna ports that the base station 105may use to support beamforming of communications with a UE 115.Likewise, a UE 115 may have one or more antenna arrays that may supportvarious MIMO or beamforming operations.

In some cases, wireless communications system 100 may be a packet-basednetwork that operate according to a layered protocol stack. In the userplane, communications at the bearer or Packet Data Convergence Protocol(PDCP) layer may be IP-based. A Radio Link Control (RLC) layer mayperform packet segmentation and reassembly to communicate over logicalchannels. A Medium Access Control (MAC) layer may perform priorityhandling and multiplexing of logical channels into transport channels.The MAC layer may also use hybrid automatic repeat request (HARM) toprovide retransmission at the MAC layer to improve link efficiency. Inthe control plane, the Radio Resource Control (RRC) protocol layer mayprovide establishment, configuration, and maintenance of an RRCconnection between a UE 115 and a base station 105 or core network 130supporting radio bearers for user plane data. At the Physical layer,transport channels may be mapped to physical channels.

Time intervals in LTE or NR may be expressed in multiples of a basictime unit, which may, for example, refer to a sampling period ofT_(s)=1/30,720,000 seconds. Time intervals of a communications resourcemay be organized according to radio frames each having a duration of 10milliseconds (ms), where the frame period may be expressed asT_(f)=307,200 T_(s). The radio frames may be identified by a systemframe number (SFN) ranging from 0 to 1023. Each frame may include 10subframes numbered from 0 to 9, and each subframe may have a duration of1 ms. A subframe may be further divided into 2 slots each having aduration of 0.5 ms, and each slot may contain 6 or 7 modulation symbolperiods (e.g., depending on the length of the cyclic prefix prepended toeach symbol period). Excluding the cyclic prefix, each symbol period maycontain 2048 sampling periods. In some cases, a subframe may be thesmallest scheduling unit of the wireless communications system 100, andmay be referred to as a transmission time interval (TTI). In othercases, a smallest scheduling unit of the wireless communications system100 may be shorter than a subframe or may be dynamically selected (e.g.,in bursts of shortened TTIs (sTTIs) or in selected component carriersusing sTTIs).

In some wireless communications systems, a slot may further be dividedinto multiple mini-slots containing one or more symbols. In someinstances, a symbol of a mini-slot or a mini-slot may be the smallestunit of scheduling. Each symbol may vary in duration depending on thesubcarrier spacing or frequency band of operation, for example. Further,some wireless communications systems may implement slot aggregation inwhich multiple slots or mini-slots are aggregated together and used forcommunication between a UE 115 and a base station 105.

The term “carrier” refers to a set of radio frequency spectrum resourceshaving a defined physical layer structure for supporting communicationsover a communication link 125. For example, a carrier of a communicationlink 125 may include a portion of a radio frequency spectrum band thatis operated according to physical layer channels for a given radioaccess technology. Each physical layer channel may carry user data,control information, or other signaling. A carrier may be associatedwith a pre-defined frequency channel (e.g., an evolved universal mobiletelecommunication system terrestrial radio access (E-UTRA) absoluteradio frequency channel number (EARFCN)), and may be positionedaccording to a channel raster for discovery by UEs 115. Carriers may bedownlink or uplink (e.g., in an FDD mode), or be configured to carrydownlink and uplink communications (e.g., in a TDD mode). In someexamples, signal waveforms transmitted over a carrier may be made up ofmultiple sub-carriers (e.g., using multi-carrier modulation (MCM)techniques such as orthogonal frequency division multiplexing (OFDM) ordiscrete Fourier transform spread OFDM (DFT-S-OFDM)).

The organizational structure of the carriers may be different fordifferent radio access technologies (e.g., LTE, LTE-A, LTE-A Pro, NR).For example, communications over a carrier may be organized according toTTIs or slots, each of which may include user data as well as controlinformation or signaling to support decoding the user data. A carriermay also include dedicated acquisition signaling (e.g., synchronizationsignals or system information, etc.) and control signaling thatcoordinates operation for the carrier. In some examples (e.g., in acarrier aggregation configuration), a carrier may also have acquisitionsignaling or control signaling that coordinates operations for othercarriers.

In some cases, a base station 105 may be a source base station 105 andmay configure one or more UEs 115 with one or more CHO configurationsfor one or more target base stations 105. The CHO configurations mayprovide, for each target base station 105, one or more associatedconditions that may trigger the UE 115 to initiate a handover to theparticular target base station 105 (e.g., based on a measurementthreshold of one or more target base station 105 measurements, one ormore source base station 105 measurements, or combinations thereof). Insome cases, the CHO configurations may include failure handlinginformation, deconfiguration criteria, or combinations thereof.

FIG. 2 illustrates an example of a wireless communications system 200with source and target base stations that supports CHO deconfigurationand failure handling in wireless communications in accordance withaspects of the present disclosure. In some examples, wirelesscommunications system 200 may implement aspects of wirelesscommunications system 100. The wireless communications system 200 mayinclude a source base station 105-a, a first target base station 105-b,and a second target base station 105-c, which may be examples of a basestation 105 described with reference to FIG. 1; and a UE 115-a, whichmay be an example of a UE 115 described with reference to FIG. 1. Thewireless communications system 200 illustrates an example of aconditional handover procedure where a communication connection betweenthe UE 115-a and the source cell served by the source base station 105-a(e.g., first base station) is handed over to one of the first targetbase station 105-b or second target base station 105-c.

Initially, the UE 115-a and the source base station 105-a may be in aconnected state and may be exchanging information over a firstcommunication connection 205. In some cases, the UE 115-a may transmitone or more measurement reports in which the UE 115-a may provide one ormore measurements for the source base station 105-a and a number ofneighboring base stations that include the first target base station105-b and the second target base station 105-c. Based in themeasurements in the measurement report, the source base station 105-amay identify one or more neighboring base stations 105 that are goodcandidates for handover of the UE 115-a (e.g., based on signal strengthmeasurements being above a threshold value). In this example, the sourcebase station 105-a may identify the first target base station 105-b andthe second target base station 105-c are handover candidates, and maycommunicate handover requests (e.g., via backhaul links 134) to eachidentified candidate. In this example, the first target base station105-b may perform admission control based on the received handoverrequest and reserve certain resources for the UE 115-a (e.g., acontention-free random access preamble, random access resources, etc.),and provide information for random access to the source base station105-a, which may be used to configure a first CHO configuration 215-a.Likewise, the second target base station 105-c may perform admissioncontrol based on the received handover request and reserve certainresources for the UE 115-a, and provide information for random access tothe source base station 105-a, which may be used to configure a secondCHO configuration 215-b.

The source base station 105-a may provide CHO configurations to the UE115-a, which may be used by the UE 115-a to autonomously initiate ahandover to a second communication connection 210. In some cases, theCHO configurations may be provided in RRC signaling (e.g., in an RRCreconfiguration message) that is transmitted to the UE 115-a. The CHOconfigurations may provide, for example, a cell ID of the associatedtarget base station 105, information for random access to the targetbase station 105 (e.g., contention-free random access resources, arandom access preamble, a cell-specific radio network temporaryidentifier (C-RNTI), etc.), and one or more measurement thresholds(e.g., RRM thresholds, channel quality metric thresholds, signalstrength metric thresholds, etc.) that are to be used to triggerhandover to the associated target base station 105. In accordance withvarious techniques provided herein, the CHO configurations provided tothe UE 115-a may also include one or more deconfiguration parameters,one or more failure handling parameters, or any combinations thereof.

In some cases, the deconfiguration parameters in CHO configurations mayprovide event-based deconfiguration and may include one or more timers,one or more deconfiguration thresholds for each CHO target base station105-b and 105-c, or any combinations thereof. Optionally, in some cases,the one or more timers may include a validity timer that starts when thehandover request is acknowledged to the source base station 105-a. Insome cases, the validity timer (e.g., valTimer_TgNB) may be maintainedby the source base station 105-a and the target base stations 105-b and105-c, and each target base station 105-b and 105-c may reserveresources for the UE 115-a during the duration of the validity timer. Inother cases, the UE 115-a may also receive an indication of the validitytimer associated with each target base station 105-b and 105-c with theCHO configurations, and may deconfigure the associated CHO configurationupon expiration of the associated validity timer. In other cases, thesource base station 105-a may transmit an explicit release of the CHOconfiguration for the target base station 105-b or 105-c with theexpired validity timer, and in such cases the UE 115-a does not need tomaintain a validity timer, or multiple validity timers for each targetbase station 105-b and 105-c. In some cases, the source base station105-a may determine a duration of the validity timer, which may be basedon estimates of UE 115-a movement, signal strength of the targetmeasured at the UE 115-a, changes in measurements at the UE 115-a overtime, estimates of a traffic load of source base station 105-a or targetbase stations 105-b or 105-c (e.g., as tracked by the respective basestation 105), or any combinations thereof.

In some cases, the CHO configurations may include one or moredeconfiguration thresholds that provide criteria for deconfiguring aCHO. In such cases, if UE 115-a measurements satisfy the threshold-basedcriteria for deconfiguration for a CHO target base station 105-b or105-c, the UE 115-a may release the CHO configuration without waitingfor an explicit indication from the source base station 105-a. Therelease of the CHO configuration may include releasing the RRCconfiguration of the target base station 105-b or 105-c, as well asassociated measurement reporting configurations corresponding tohandover trigger and CHO deconfiguration trigger. In some cases, the UE115-a may transmit a measurement report to the source base station 105-aso that the network is informed of the deconfiguration and the targetbase station 105-b or 105-c may release reserved resources for the UE115-a. In some cases, the measurement report (e.g., a RRC measurementreport message) may include a deconfiguration indication (e.g., a cellID of the deconfigured target base station 105-b or 105-c). Upondeconfiguring the CHO configuration for the target base station 105-b or105-c, the UE 115-a may discontinue performing measurements on andevaluating whether the target base station 105-b or 105-c meets thehandover or CHO deconfiguration criteria. In some cases, one or moremeasurement events may be defined for CHO deconfiguration. In someexample, such measurement events may include Event 1, where a neighborcell measurement (e.g., a signal strength, channel quality metric, etc.)drops below a threshold value; Event 2, where the source base station105-a (e.g., a source primary cell (SpCell)) measurement becomes betterthan a first threshold value and a target base station 105-b or 105-cmeasurement becomes worse than a second threshold value; Event 3, wherea measurement offset between a target base station 105-b or 105-smeasurement and the source base station 105-a exceeds an offsetthreshold value; or any combinations thereof. Upon detection of one ormore of the measurement events, the UE 115-a may release the associatedCHO configuration, and provide a measurement report (e.g., that containsan indication of the deconfiguration) to the source base station 105-a.In some cases, the measurement thresholds configured in each CHO may bedifferent for each target base station 105-b and 105-c.

In some cases, the CHO configurations may, additionally oralternatively, include one or more timers for use in detecting a failureof a handover. In some cases, the one or more timers may include aconditional handover timer (e.g., CHO_timer_TgNB) that is initiated bythe UE 115-a upon transmission of a random access request of a handoverprocedure. In such cases, the UE 115-a may determine, for example, thatCHO criteria for a handover from the source base station 105-a to thefirst target base station 105-b is satisfied, and may transmit therandom access request to the first target base station 105-a and startthe conditional handover timer. If the conditional handover timerexpires prior to the UE 115-a establishing a connection with the firsttarget base station 105-b, the UE 115-a may assume that the randomaccess procedure has failed and initiate failure handling. In caseswhere the UE 115-a maintains a validity timer for the first target basestation 105-b, the UE 115-a may stop the validity timer upontransmitting the random access request. In some cases, the failurehandling may include selecting the second target base station 105-c(e.g., or another base station with a CHO configuration where the UE115-a meets CHO criteria for initiating a handover), and transmitting arandom access request to the second target base station 105-c. The UE115-c may initiate a second conditional access timer associated with thesecond target base station 105-c, and the process may continue until asuccessful random access procedure is performed, or until the UE 115-aruns out of CHO targets that meet CHO criteria, at which point the basestation 105-b may declare a radio link failure and initiate a RRCre-establishment procedure. In some cases, the conditional handovertimer may be different for each of the different target base stations.Table 1 below includes an example of conditional handover timer startcriteria, stop criteria, and failure actions to take in the event ofconditional handover timer expiration.

TABLE 1 CHO failure handling timer CHO_timer_TgNB CHO_timer_TgNB startstop Upon CHO_timer_TgNB expiry Upon initiating Upon successful Stopongoing random access procedure on the random access on a completion ofCHO target cell. CHO target cell, random access If there are targetcells for which CHO has which meets the procedure on the been triggeredand for which the validity CHO triggering CHO target cell. timer (ifconfigured) has not expired, UE criteria. initiates handover to thesecells (one at a time). If there are no such target cells remaining, UEperforms the RRC re-establishment procedure.

FIG. 3 illustrates an example of a general process flow 300 for CHO,that supports CHO deconfiguration and failure handling in wirelesscommunications in accordance with aspects of the present disclosure. Insome examples, process flow 300 may implement aspects of wirelesscommunications system 100 or 200. The process flow in this exampleincludes a UE 115-b, which may be an example of a UE described withreference to FIGS. 1 and 2; a source base station 105-d, a first targetbase station 105-e, and a second target base station 105-f, which may beexamples of base stations described with reference to FIGS. 1 and 2. Theprocess flow 300 includes functions and communications implemented by UE115-b and base stations 105-d, 105-e, and 105-f in the context ofconditional handover procedures.

In the following description of the process flow 300, the operationsbetween UE 115-b and base station 105-d, 105-e, and 105-f may betransmitted in a different order than the order shown, or the operationsmay be performed in different orders or at different times. Certainoperations may also be left out of the process flow 300, or otheroperations may be added to the process flow 300. It is to be understoodthat while base stations 105 and UE 115-b are shown performing a numberof the operations of process flow 300, any wireless device may performthe operations shown.

At 305, the UE 115-b may transmit a measurement report to the sourcebase station 105-d. The measurement report may include one or morechannel measurements for the source base station 105-d, as well asmeasurements for multiple neighboring base stations, which may includethe first target base station 105-e and the second target base station105-f. The measurement report may be a “low” threshold measurementreport, which may indicate that a channel measurement associated withthe source base station 105-d is below a threshold value that is used toindicate that the source base station 105-d should configure a CHO forthe UE 115-b.

At 310, the source base station 105-d may transmit a handover request tothe first target base station 105-e. Further, at 315, the source basestation 105-d may transmit a handover request to the second target basestation 105-f. In some cases, the source base station 105-d may selectthe first target base station 105-e and the second target base station105-f for the handover requests based on associated measurements fromthe measurement report of the UE 115-b (e.g., based on neighboring basestation measurements that are above a threshold value or that are betterthan other of the neighboring base station measurements). While thisexample shows two target base stations 105, more or fewer target basestations 105 may be identified for CHO configuration. In some cases, thehandover requests may include handover information associated with theUE 115-b, and may also include a time duration for a validity timer asdiscussed herein.

At 320, the first target base station 105-e may perform admissioncontrol responsive to receiving the handover request. Likewise, at 325,the second target base station 105-f may perform admission controlresponsive to receiving the handover request. The admission control maydetermine that resources may be reserved for the UE 115-c (e.g., aC-RNTI, contention free random access resources, random access preamble,etc.).

At 330, the first target base station 105-e may transmit a handoverrequest acknowledgment to the source base station 105-d. Further, inthis example, at 335, the second target base station 105-f may transmita handover request acknowledgment to the source base station 105-d. Thehandover request acknowledgments may include information for use by theUE 115-b to establish a connection (e.g., random access preamble,C-RNTI, etc.). The source base station 105-d may receive the handoverrequest acknowledgments, and determine CHO criteria for each target cellfor use by the UE 115-b to trigger a CHO. The CHO criteria may include,for example, one or more measurement thresholds of the associated targetbase station 105, the source base station 105-d, or any combinationsthereof.

At 340, the source base station 105-d may transmit CHO configurationinformation to the UE 115-b in a RRC reconfiguration message. In somecases, the RRC reconfiguration message may indicate that the firsttarget base station 105-e and the second target base station 105-f areconfigured for CHO, may provide information for accessing the associatedbase stations 105 (e.g., random access information, C-RNTI, etc.), andmay provide handover thresholds associated with each target base station105.

At 345, the UE 115-b may determine that a condition for handover to thefirst target base station 105-d is met. Such a determination may bemade, for example, based on one or more channel quality measurements ofthe UE 115-b that are compared to the CHO configurations provided by thesource base station 105-d. At 350, the UE 115-b may initiate a randomaccess channel (RACH) procedure with the first target base station 105-eand perform the handover procedure.

FIG. 4 illustrates an example of a process flow 400 for configuring andthen releasing a CHO configuration in wireless communications inaccordance with aspects of the present disclosure. In some examples,process flow 400 may implement aspects of wireless communications system100 or 200. The process flow in this example includes a UE 115-c, whichmay be an example of a UE described with reference to FIGS. 1 and 2; asource base station 105-g, and a target base station 105-h, which may beexamples of base stations described with reference to FIGS. 1 and 2. Theprocess flow 400 includes functions and communications implemented by UE115-c and base stations 105-g, and 105-h in the context of conditionalhandover procedures.

In the following description of the process flow 400, the operationsbetween UE 115-c and base station 105-g and 105-h may be transmitted ina different order than the order shown, or the operations may beperformed in different orders or at different times. Certain operationsmay also be left out of the process flow 400, or other operations may beadded to the process flow 400. It is to be understood that while basestations 105 and UE 115-c are shown performing a number of theoperations of process flow 400, any wireless device may perform theoperations shown.

At 405, the UE 115-c may transmit a measurement report to the sourcebase station 105-g. The measurement report may include one or morechannel measurements for the source base station 105-g, as well asmeasurements for multiple neighboring base stations, which may includethe target base station 105-h. The measurement report may be a “low”threshold measurement report, which may indicate that a channelmeasurement associated with the source base station 105-g is below athreshold value that is used to indicate that the source base station105-g should configure a CHO for the UE 115-c.

At 410, the source base station 105-g may transmit a handover request tothe target base station 105-h. While the example of FIG. 4 illustrates asingle target base station 105-h, in other cases multiple differenttarget base stations may be configured for CHO and the operations ofFIG. 4 may be used for any number of target base stations. In somecases, the source base station 105-g may select the target base station105-h for the handover request based on associated measurements from themeasurement report of the UE 115-c (e.g., based on neighboring basestation measurements that are above a threshold value or that are betterthan other of the neighboring base station measurements). In some cases,the handover request may include handover information associated withthe UE 115-c, and may also include a time duration for a validity timeras discussed herein.

At 415, the target base station 105-h may perform admission controlresponsive to receiving the handover request. The admission control maydetermine that resources may be reserved for the UE 115-c (e.g., aC-RNTI, contention free random access resources, random access preamble,etc.).

At 420, the target base station 105-h may transmit a handover requestacknowledgment to the source base station 105-g. The handover requestacknowledgment may include information for use by the UE 115-c toestablish a connection (e.g., random access preamble, C-RNTI, etc.) withthe target base station 105-h. The source base station 105-g may receivethe handover request acknowledgment, and determine CHO criteria for thetarget cell for use by the UE 115-c to trigger a CHO. The CHO criteriamay include, for example, one or more measurement thresholds (e.g.,measThreshHO_TgNB) of the target base station 105-h (and for any otherconfigured target base stations), the source base station 105-g, or anycombinations thereof.

At 425, the source base station 105-g may transmit CHO configurationinformation to the UE 115-c in a RRC reconfiguration message. In somecases, the RRC reconfiguration message may indicate that the target basestation 105-h is configured for CHO, may provide information foraccessing the associated base stations 105 (e.g., random accessinformation, C-RNTI, etc.), and may provide handover thresholdsassociated with each the target base station 105-h.

At 430, the source base station may determine that the UE 115-c ismoving away from the target base station 105-h. In some cases, such adetermination may be made based on one or more measurement reportsprovided by the UE 115-c, based on signal strength measurements of theUE 115-c, positioning information of the UE 115-c, and the like.

At 435, the source base station 105-g may transmit another RRCreconfiguration to the UE 115-c to release the CHO configuration for thetarget base station 105-h. At 440, the source base station 105-g maytransmit a handover cancellation to the target base station 105-h tocancel the CHO configuration. The UE 115-c and the target base station105-h may delete the CHO configuration based on the signaling from thesource base station 105-g.

FIG. 5 illustrates an example of a process flow 500 that supports CHOdeconfiguration and failure handling in wireless communications inaccordance with aspects of the present disclosure. In some examples,process flow 500 may implement aspects of wireless communications system100 or 200. The process flow in this example includes a UE 115-d, whichmay be an example of a UE described with reference to FIGS. 1 and 2; asource base station 105-i, and a target base station 105-j, which may beexamples of base stations described with reference to FIGS. 1 and 2. Theprocess flow 500 includes functions and communications implemented by UE115-d and base stations 105-i, and 105-j in the context of conditionalhandover procedures.

In the following description of the process flow 500, the operationsbetween UE 115-d and base station 105-i and 105-j may be transmitted ina different order than the order shown, or the operations may beperformed in different orders or at different times. Certain operationsmay also be left out of the process flow 500, or other operations may beadded to the process flow 500. It is to be understood that while basestations 105 and UE 115-d are shown performing a number of theoperations of process flow 500, any wireless device may perform theoperations shown.

At 505, the UE 115-d may transmit a measurement report to the sourcebase station 105-i. The measurement report may include one or morechannel measurements for the source base station 105-i, as well asmeasurements for multiple neighboring base stations, which may includethe target base station 105-j. The measurement report may be a “low”threshold measurement report, which may indicate that a channelmeasurement associated with the source base station 105-i is below athreshold value that is used to indicate that the source base station105-i should configure a CHO for the UE 115-d.

At 510, the source base station 105-i may transmit a handover request tothe target base station 105-j. While the example of FIG. 5 illustrates asingle target base station 105-j, in other cases multiple differenttarget base stations may be configured for CHO and the operations ofFIG. 5 may be used for any number of target base stations. In somecases, the source base station 105-i may select the target base station105-j for the handover request based on associated measurements from themeasurement report of the UE 115-d (e.g., based on neighboring basestation measurements that are above a threshold value or that are betterthan other of the neighboring base station measurements). In some cases,the handover request may include handover information associated withthe UE 115-d, and may also optionally include a time duration for avalidity timer 540. In cases where multiple CHO configurations formultiple target base stations are configured, multiple differentvalidity timers may be present for the different target base stations.

At 515, the target base station 105-j may perform admission controlresponsive to receiving the handover request. The admission control maydetermine that resources may be reserved for the UE 115-d (e.g., aC-RNTI, contention free random access resources, random access preamble,etc.).

At 520, the target base station 105-j may transmit a handover requestacknowledgment to the source base station 105-i. The handover requestacknowledgment may include information for use by the UE 115-d toestablish a connection (e.g., random access preamble, C-RNTI, etc.) withthe target base station 105-j. The source base station 105-i may receivethe handover request acknowledgment, and determine CHO criteria for thetarget cell for use by the UE 115-d to trigger a CHO. The CHO criteriamay include, for example, one or more measurement thresholds (e.g.,measThreshHO_TgNB) of the target base station 105-j (and for any otherconfigured target base stations), the source base station 105-i, or anycombinations thereof. In this example, the CHO criteria may also includea validity time duration (e.g., calTimer_TgNB) for the target basestation 105-j.

At 525, the source base station 105-i may transmit CHO configurationinformation to the UE 115-d in a RRC reconfiguration message. In somecases, the RRC reconfiguration message may indicate that the target basestation 105-j is configured for CHO, may provide information foraccessing the associated base stations 105 (e.g., random accessinformation, C-RNTI, etc.), and may provide handover thresholdsassociated with each the target base station 105-j. In cases where theCHO configuration provided to the UE 115-d includes a validity timer,the UE 115-d may start the validity timer 540 associated with the targetbase station 105-j. In some cases, the source base station 105-i and thetarget base station 105-j may keep validity timers, and the UE 115-d maynot keep the validity timer 540, which may simplify implementation atthe UE 115-d. In such cases, upon expiration of the validity timer, thesource base station 105-i may explicitly release the CHO through anotherRRC reconfiguration message. In cases where the UE 115-d keeps thevalidity timer 540, the UE 115-d may autonomously release the CHOconfiguration upon expiration of the validity timer 540, and the basestations 105 may also release the CHO configuration based on validitytimers kept at the base stations 105.

At 530, the UE 115-d may determine that the condition for handover ismet while the validity timer is valid. Such a determination may be made,for example, based on one or more channel quality measurements of the UE115-d that are compared to the CHO configuration provided by the sourcebase station 105-i. At 535, the UE 115-d may initiate a RACH procedurewith the first target base station 105-e and perform the handoverprocedure with the target base station 105-j.

FIG. 6 illustrates an example of a process flow 600 that supports CHOdeconfiguration and failure handling in wireless communications inaccordance with aspects of the present disclosure. In some examples,process flow 600 may implement aspects of wireless communications system100 or 200. The process flow in this example includes a UE 115-e, whichmay be an example of a UE described with reference to FIGS. 1 and 2; asource base station 105-k, a first target base station 105-l, and asecond target base station 105-m, which may be examples of base stationsdescribed with reference to FIGS. 1 and 2. The process flow 600 includesfunctions and communications implemented by UE 115-e and base stations105-k, 105-l, and 105-m in the context of conditional handoverprocedures.

In the following description of the process flow 600, the operationsbetween UE 115-e and base station 105-k, 105-l, and 105-m may betransmitted in a different order than the order shown, or the operationsmay be performed in different orders or at different times. Certainoperations may also be left out of the process flow 600, or otheroperations may be added to the process flow 600. It is to be understoodthat while base stations 105 and UE 115-e are shown performing a numberof the operations of process flow 600, any wireless device may performthe operations shown.

At 605, the UE 115-e may transmit a measurement report to the sourcebase station 105-k. The measurement report may include one or morechannel measurements for the source base station 105-k, as well asmeasurements for multiple neighboring base stations, which may includethe first target base station 105-l and the second target base station105-m. The measurement report may be a “low” threshold measurementreport, which may indicate that a channel measurement associated withthe source base station 105-k is below a threshold value that is used toindicate that the source base station 105-k should configure a CHO forthe UE 115-e.

At 610, the source base station 105-k, the first target base station105-l, and the second target base station 105-m may perform targethandover preparation (e.g., based on handover requests, admissioncontrol, and handover request acknowledgments). The handover preparationmay include determination of information for use by the UE 115-e toestablish a connection (e.g., random access preambles, C-RNTIs, etc.).The source base station 105-k may determine CHO criteria for each targetcell for use by the UE 115-e to trigger a CHO. The CHO criteria mayinclude, for example, one or more measurement thresholds of theassociated target base station 105, the source base station 105-k, orany combinations thereof. In this example, the CHO configuration mayalso include a CHO timer for each target base station 105-l and 105-m.In some cases, the base stations 105 may keep validity timers 620, andmay release CHO configurations of target cells upon expiry of anassociated validity timer.

At 615, the source base station 105-k may transmit CHO configurationinformation to the UE 115-e in a RRC reconfiguration message. In somecases, the RRC reconfiguration message may indicate that the firsttarget base station 105-l and the second target base station 105-m areconfigured for CHO, may provide information for accessing the associatedbase stations 105 (e.g., random access information, C-RNTI, etc.), andmay provide handover thresholds associated with each target base station105.

At 625, the UE 115-e may determine that a condition for handover to thefirst target base station 105-l is met. Such a determination may bemade, for example, based on one or more channel quality measurements ofthe UE 115-e that are compared to the CHO configurations provided by thesource base station 105-k. At 630, the UE 115-e may initiate a randomaccess channel (RACH) procedure with the first target base station105-l, and start CHO timer 635 associated with the first target basestation 105-l upon transmission of an initial random access requestmessage. In this example, at 640, the UE 115-e may determine a CHOfailure based on an expiration of the CHO timer 635 prior to completingthe random access procedure with the first target base station 105-l.For example, the UE 115-e may not receive a random access response afterone or more retransmissions of the random access request while the CHOtimer 635 is valid.

At 645, the UE 115-e may determine that a condition for handover to thesecond target base station 105-m is met. Such a determination may bemade, for example, based on one or more channel quality measurements ofthe UE 115-e that are compared to the CHO configurations provided by thesource base station 105-k while the CHO configuration of the secondtarget base station 105-m is active. At 655, the UE 115-e may initiate arandom access channel (RACH) procedure with the first target basestation 105-l, and start CHO timer 650 associated with the second targetbase station 105-m upon transmission of an initial random access requestmessage. In this example, the random access procedure with the secondtarget base station 105-m may be successful, and the UE 115-e maycomplete the handover. In cases where the CHO timer 650 expires prior tocompleting the random access procedure with the second target basestation 105-m, the UE 115-e may repeat the process for any other targetbase stations having an active CHO configuration. In cases wheremultiple target base stations have CHO configuration and meet conditionsfor handover, the UE 115-e may select one based on one or morepredetermined criteria (e.g., the target base station with a highestchannel quality, the target base station having the shortest timeremaining on a validity timer, an earliest configured CHO, etc.). Incases where there is a CHO failure and no other target base stations areconfigured for CHO, the UE 115-e may declare a radio link failure andinitiate a RRC connection re-establishment procedure.

FIG. 7 illustrates an example of a process flow 700 that supports CHOdeconfiguration and failure handling in wireless communications inaccordance with aspects of the present disclosure. In some examples,process flow 700 may implement aspects of wireless communications system100 or 200. The process flow in this example includes a UE 115-f, whichmay be an example of a UE described with reference to FIGS. 1 and 2; asource base station 105-n, and a target base station 105-o, which may beexamples of base stations described with reference to FIGS. 1 and 2. Theprocess flow 700 includes functions and communications implemented by UE115-f and base stations 105-n, and 105-o in the context of conditionalhandover procedures.

In the following description of the process flow 700, the operationsbetween UE 115-f and base station 105-n and 105-o may be transmitted ina different order than the order shown, or the operations may beperformed in different orders or at different times. Certain operationsmay also be left out of the process flow 700, or other operations may beadded to the process flow 700. It is to be understood that while basestations 105 and UE 115-f are shown performing a number of theoperations of process flow 700, any wireless device may perform theoperations shown.

At 705, the UE 115-f may transmit a measurement report to the sourcebase station 105-n. The measurement report may include one or morechannel measurements for the source base station 105-n, as well asmeasurements for multiple neighboring base stations, which may includethe target base station 105-o. The measurement report may be a “low”threshold measurement report, which may indicate that a channelmeasurement associated with the source base station 105-n is below athreshold value that is used to indicate that the source base station105-n should configure a CHO for the UE 115-f.

At 710, the source base station 105-n may transmit a handover request tothe target base station 105-o. While the example of FIG. 7 illustrates asingle target base station 105-o, in other cases multiple differenttarget base stations may be configured for CHO and the operations ofFIG. 7 may be used for any number of target base stations. In somecases, the source base station 105-n may select the target base station105-o for the handover request based on associated measurements from themeasurement report of the UE 115-f (e.g., based on neighboring basestation measurements that are above a threshold value or that are betterthan other of the neighboring base station measurements). In some cases,the handover request may include handover information associated withthe UE 115-f.

At 715, the target base station 105-o may perform admission controlresponsive to receiving the handover request. The admission control maydetermine that resources may be reserved for the UE 115-f (e.g., aC-RNTI, contention free random access resources, random access preamble,etc.).

At 720, the target base station 105-o may transmit a handover requestacknowledgment to the source base station 105-n. The handover requestacknowledgment may include information for use by the UE 115-f toestablish a connection (e.g., random access preamble, C-RNTI, etc.) withthe target base station 105-o. The source base station 105-n may receivethe handover request acknowledgment, and determine CHO criteria for thetarget cell for use by the UE 115-f to trigger a CHO. The CHO criteriamay include, for example, one or more measurement thresholds (e.g.,measThreshHO_TgNB) of the target base station 105-o (and for any otherconfigured target base stations), the source base station 105-n, or anycombinations thereof. In this example, the CHO criteria may also includeone or more deconfiguration criteria (e.g., measThreshDeconfig_TgNB)which, if met, trigger deconfiguration of the CHO. In some cases, theCHO criteria may also include a, and may also include a time durationfor one or more timers (e.g., a validity timer, CHO timer, or both).

At 725, the source base station 105-n may transmit CHO configurationinformation to the UE 115-f in a RRC reconfiguration message. In somecases, the RRC reconfiguration message may indicate that the target basestation 105-o is configured for CHO, may provide information foraccessing the associated base stations 105 (e.g., random accessinformation, C-RNTI, etc.), and may provide handover thresholds anddeconfiguration thresholds associated with each the target base station105-o.

At 730, the UE 115-f may determine that the condition for target basestation 105-o deconfiguration is met. Such a determination may be made,for example, based on one or more channel quality measurements of the UE115-f that are compared to the CHO configuration provided by the sourcebase station 105-n. At 735, the UE 115-f may transmit a measurementreport to the source base station 105-n. In some cases, the measurementreport may indicate that the CHO configuration for the target basestation 105-o is deconfigured. The CHO deconfiguration may includereleasing the RRC configuration of the target base station 105-o, andthe UE 115-f may discontinue performing measurements on and evaluatingwhether the target base station 105-o meets the handover or CHOdeconfiguration criteria. In some cases, the measurement report (e.g., aRRC measurement report message) may include a deconfigurationindication.

At 740, the source base station 105-n may transmit a handover cancelindication to the target base station 105-o. The target base station105-o, at 745, may release resources reserved for the UE 115-fresponsive to the handover cancel indication.

FIG. 8 shows a block diagram 800 of a device 805 that supports CHOdeconfiguration and failure handling in wireless communications inaccordance with aspects of the present disclosure. The device 805 may bean example of aspects of a UE 115 as described herein. The device 805may include a receiver 810, a communications manager 815, and atransmitter 820. The device 805 may also include a processor. Each ofthese components may be in communication with one another (e.g., via oneor more buses).

The receiver 810 may receive information such as packets, user data, orcontrol information associated with various information channels (e.g.,control channels, data channels, and information related to CHOdeconfiguration and failure handling in wireless communications, etc.).Information may be passed on to other components of the device 805. Thereceiver 810 may be an example of aspects of the transceiver 1120described with reference to FIG. 11. The receiver 810 may utilize asingle antenna or a set of antennas.

The communications manager 815 may receive, from a source base station,a conditional handover configuration that indicates one or more targetbase stations, one or more measurement thresholds for initiating ahandover from the source base station to the one or more target basestations, and one or more timers associated with the handover to the oneor more target base stations, determine a first conditional handoverfailure responsive to the first conditional handover timer expiringprior to completing the first random access procedure, determine, basedon the conditional handover configuration, that a first measurementthreshold for initiating the handover to a first target base station issatisfied, transmit, based on the conditional handover configuration, afirst random access request to the first target base station to initiatea first random access procedure for the handover to the first targetbase station, and start a first conditional handover timer forcompleting the first random access procedure responsive to thetransmitting the first random access request.

The communications manager 815 may also receive, from a source basestation, a conditional handover configuration that indicates one or moreconditional handover configurations associated with one or more targetbase stations, where each of the one or more conditional handoverconfigurations include a triggering measurement threshold for initiatinga conditional handover to an associated target base station and adeconfiguration measurement threshold for deconfiguring the conditionalhandover configuration of the associated target base station, releasethe first conditional handover configuration of the first target basestation, and determine, based on the conditional handover configuration,that a first deconfiguration measurement threshold for deconfiguring afirst conditional handover configuration of a first target base stationis satisfied. The communications manager 815 may be an example ofaspects of the communications manager 1110 described herein.

The communications manager 815, or its sub-components, may beimplemented in hardware, code (e.g., software or firmware) executed by aprocessor, or any combination thereof. If implemented in code executedby a processor, the functions of the communications manager 815, or itssub-components may be executed by a general-purpose processor, a DSP, anapplication-specific integrated circuit (ASIC), a FPGA or otherprogrammable logic device, discrete gate or transistor logic, discretehardware components, or any combination thereof designed to perform thefunctions described in the present disclosure.

The communications manager 815, or its sub-components, may be physicallylocated at various positions, including being distributed such thatportions of functions are implemented at different physical locations byone or more physical components. In some examples, the communicationsmanager 815, or its sub-components, may be a separate and distinctcomponent in accordance with various aspects of the present disclosure.In some examples, the communications manager 815, or its sub-components,may be combined with one or more other hardware components, includingbut not limited to an input/output (I/O) component, a transceiver, anetwork server, another computing device, one or more other componentsdescribed in the present disclosure, or a combination thereof inaccordance with various aspects of the present disclosure.

The transmitter 820 may transmit signals generated by other componentsof the device 805. In some examples, the transmitter 820 may becollocated with a receiver 810 in a transceiver module. For example, thetransmitter 820 may be an example of aspects of the transceiver 1120described with reference to FIG. 11. The transmitter 820 may utilize asingle antenna or a set of antennas.

FIG. 9 shows a block diagram 900 of a device 905 that supports CHOdeconfiguration and failure handling in wireless communications inaccordance with aspects of the present disclosure. The device 905 may bean example of aspects of a device 805, or a UE 115 as described herein.The device 905 may include a receiver 910, a communications manager 915,and a transmitter 940. The device 905 may also include a processor. Eachof these components may be in communication with one another (e.g., viaone or more buses).

The receiver 910 may receive information such as packets, user data, orcontrol information associated with various information channels (e.g.,control channels, data channels, and information related to CHOdeconfiguration and failure handling in wireless communications, etc.).Information may be passed on to other components of the device 905. Thereceiver 910 may be an example of aspects of the transceiver 1120described with reference to FIG. 11. The receiver 910 may utilize asingle antenna or a set of antennas.

The communications manager 915 may be an example of aspects of thecommunications manager 815 as described herein. The communicationsmanager 915 may include a handover configuration manager 920, ameasurement manager 925, a random access manager 930, and a conditionalhandover timer 935. The communications manager 915 may be an example ofaspects of the communications manager 1110 described herein.

The handover configuration manager 920 may receive, from a source basestation, a conditional handover configuration that indicates one or moretarget base stations, one or more measurement thresholds for initiatinga handover from the source base station to the one or more target basestations, and one or more timers associated with the handover to the oneor more target base stations and determine a first conditional handoverfailure responsive to the first conditional handover timer expiringprior to completing the first random access procedure.

The measurement manager 925 may determine, based on the conditionalhandover configuration, that a first measurement threshold forinitiating the handover to a first target base station is satisfied.

The random access manager 930 may transmit, based on the conditionalhandover configuration, a first random access request to the firsttarget base station to initiate a first random access procedure for thehandover to the first target base station.

The conditional handover timer 935 may start a first conditionalhandover timer for completing the first random access procedureresponsive to the transmitting the first random access request.

In some cases, the handover configuration manager 920 may receive, froma source base station, a conditional handover configuration thatindicates one or more conditional handover configurations associatedwith one or more target base stations, where each of the one or moreconditional handover configurations include a triggering measurementthreshold for initiating a conditional handover to an associated targetbase station and a deconfiguration measurement threshold fordeconfiguring the conditional handover configuration of the associatedtarget base station and release the first conditional handoverconfiguration of the first target base station.

The measurement manager 925 may determine, based on the conditionalhandover configuration, that a first deconfiguration measurementthreshold for deconfiguring a first conditional handover configurationof a first target base station is satisfied.

The transmitter 940 may transmit signals generated by other componentsof the device 905. In some examples, the transmitter 940 may becollocated with a receiver 910 in a transceiver module. For example, thetransmitter 940 may be an example of aspects of the transceiver 1120described with reference to FIG. 11. The transmitter 940 may utilize asingle antenna or a set of antennas.

FIG. 10 shows a block diagram 1000 of a communications manager 1005 thatsupports CHO deconfiguration and failure handling in wirelesscommunications in accordance with aspects of the present disclosure. Thecommunications manager 1005 may be an example of aspects of acommunications manager 815, a communications manager 915, or acommunications manager 1110 described herein. The communications manager1005 may include a handover configuration manager 1010, a measurementmanager 1015, a random access manager 1020, a conditional handover timer1025, an optional validity timer 1030, and a RRC connectionestablishment component 1035. Each of these modules may communicate,directly or indirectly, with one another (e.g., via one or more buses).

The handover configuration manager 1010 may receive, from a source basestation, a conditional handover configuration that indicates one or moretarget base stations, one or more measurement thresholds for initiatinga handover from the source base station to the one or more target basestations, and one or more timers associated with the handover to the oneor more target base stations.

In some examples, the handover configuration manager 1010 may determinea first conditional handover failure responsive to the first conditionalhandover timer expiring prior to completing the first random accessprocedure.

In some examples, the handover configuration manager 1010 may receive,from a source base station, a conditional handover configuration thatindicates one or more conditional handover configurations associatedwith one or more target base stations, where each of the one or moreconditional handover configurations include a triggering measurementthreshold for initiating a conditional handover to an associated targetbase station and a deconfiguration measurement threshold fordeconfiguring the conditional handover configuration of the associatedtarget base station. In some examples, the handover configurationmanager 1010 may release the first conditional handover configuration ofthe first target base station.

In some examples, the handover configuration manager 1010 may repeat thedetermining, transmitting, and starting timers for any other target basestations configured for conditional handover upon further conditionalhandover failures.

In some examples, the handover configuration manager 1010 may select,responsive to the first conditional handover timer expiring, the secondtarget base station from a set of available target base stations basedon one or more of a channel quality measurement associated with each ofthe set of available target base stations, an amount of time remainingon a validity timer associated with each of the set of available targetbase stations, or any combinations thereof.

In some examples, the handover configuration manager 1010 may delete oneor more of a radio resource control configuration, a first measurementand reporting configuration for conditional handover trigger andconditional handover deconfiguration trigger, or one or more timersassociated with the first target base station, that are provided in thefirst conditional handover configuration.

In some examples, the handover configuration manager 1010 maydiscontinue conditional handover measurements associated with the firsttarget base station and evaluating whether the measurements meetconditional handover criteria or conditional handover deconfigurationcriteria. In some cases, the one or more timers include at least thefirst conditional handover timer for completing the first random accessprocedure with the first target base station.

In some cases, the first deconfiguration measurement threshold is achannel quality threshold associated with the first target base station,and where the first conditional handover configuration is releasedresponsive to a channel quality measurement of the first target basestation being below the channel quality threshold. In some cases, thefirst deconfiguration measurement threshold includes a first thresholdvalue associated with the source base station and a second thresholdvalue associated with the first target base station, and where the firstconditional handover configuration is released responsive to a firstchannel quality measurement of the source base station exceeding thefirst threshold and a second channel quality measurement of the firsttarget base station being below the second threshold value. In somecases, the first deconfiguration measurement threshold is a differencethreshold, and where the first conditional handover configuration isreleased responsive to a difference between channel quality measurementsof the source base station and the first target base station exceedingthe difference threshold.

The measurement manager 1015 may determine, based on the conditionalhandover configuration, that a first measurement threshold forinitiating the handover to a first target base station is satisfied.

In some examples, the measurement manager 1015 may determine, based onthe conditional handover configuration, that a first deconfigurationmeasurement threshold for deconfiguring a first conditional handoverconfiguration of a first target base station is satisfied.

In some examples, the measurement manager 1015 may determine, responsiveto the first conditional handover timer expiring, that a secondmeasurement threshold for initiating a handover to a second target basestation is satisfied.

In some examples, the measurement manager 1015 may determine, based onthe conditional handover configuration, that a second triggeringmeasurement threshold for initiating a handover to a second target basestation is satisfied.

In some examples, the measurement manager 1015 may transmit ameasurement report to the source base station that indicates the firstconditional handover configuration of the first target base station isreleased. In some cases, the measurement report contains adeconfiguration indication for the first target base station.

The random access manager 1020 may transmit, based on the conditionalhandover configuration, a first random access request to the firsttarget base station to initiate a first random access procedure for thehandover to the first target base station.

In some examples, the random access manager 1020 may transmit, based onthe conditional handover configuration, a second random access requestto the second target base station to initiate a second random accessprocedure for the handover to the second target base station.

The conditional handover timer 1025 may start a first conditionalhandover timer for completing the first random access procedureresponsive to the transmitting the first random access request. In someexamples, the conditional handover timer 1025 may start a secondconditional handover timer for completing the second random accessprocedure. In some cases, a first duration of the first conditionalhandover timer is different than a second duration of the secondconditional handover timer.

The validity timer 1030, if present, may initiate, responsive toreceiving the conditional handover configuration, the first validitytimer and the second validity timer. In some examples, the validitytimer 1030 may delete the second conditional handover configurationresponsive to an expiration of the second validity timer. In someexamples, the validity timer 1030 may stop the first validity timer upontransmitting the first random access request to the first target basestation.

The RRC connection establishment component 1035 may initiate aconnection re-establishment procedure upon determining that no othertarget base stations are configured for conditional handover.

FIG. 11 shows a diagram of a system 1100 including a device 1105 thatsupports CHO deconfiguration and failure handling in wirelesscommunications in accordance with aspects of the present disclosure. Thedevice 1105 may be an example of or include the components of device805, device 905, or a UE 115 as described herein. The device 1105 mayinclude components for bi-directional voice and data communicationsincluding components for transmitting and receiving communications,including a communications manager 1110, an I/O controller 1115, atransceiver 1120, an antenna 1125, memory 1130, and a processor 1140.These components may be in electronic communication via one or morebuses (e.g., bus 1145).

The communications manager 1110 may receive, from a source base station,a conditional handover configuration that indicates one or more targetbase stations, one or more measurement thresholds for initiating ahandover from the source base station to the one or more target basestations, and one or more timers associated with the handover to the oneor more target base stations, determine a first conditional handoverfailure responsive to the first conditional handover timer expiringprior to completing the first random access procedure, determine, basedon the conditional handover configuration, that a first measurementthreshold for initiating the handover to a first target base station issatisfied, transmit, based on the conditional handover configuration, afirst random access request to the first target base station to initiatea first random access procedure for the handover to the first targetbase station, and start a first conditional handover timer forcompleting the first random access procedure responsive to thetransmitting the first random access request.

The communications manager 1110 may also receive, from a source basestation, a conditional handover configuration that indicates one or moreconditional handover configurations associated with one or more targetbase stations, where each of the one or more conditional handoverconfigurations include a triggering measurement threshold for initiatinga conditional handover to an associated target base station and adeconfiguration measurement threshold for deconfiguring the conditionalhandover configuration of the associated target base station, releasethe first conditional handover configuration of the first target basestation, and determine, based on the conditional handover configuration,that a first deconfiguration measurement threshold for deconfiguring afirst conditional handover configuration of a first target base stationis satisfied.

The I/O controller 1115 may manage input and output signals for thedevice 1105. The I/O controller 1115 may also manage peripherals notintegrated into the device 1105. In some cases, the I/O controller 1115may represent a physical connection or port to an external peripheral.In some cases, the I/O controller 1115 may utilize an operating systemsuch as iOS®, ANDROID®, MS-DOS®, MS-WINDOWS®, OS/2®, UNIX®, LINUX®, oranother known operating system. In other cases, the I/O controller 1115may represent or interact with a modem, a keyboard, a mouse, atouchscreen, or a similar device. In some cases, the I/O controller 1115may be implemented as part of a processor. In some cases, a user mayinteract with the device 1105 via the I/O controller 1115 or viahardware components controlled by the I/O controller 1115.

The transceiver 1120 may communicate bi-directionally, via one or moreantennas, wired, or wireless links as described above. For example, thetransceiver 1120 may represent a wireless transceiver and maycommunicate bi-directionally with another wireless transceiver. Thetransceiver 1120 may also include a modem to modulate the packets andprovide the modulated packets to the antennas for transmission, and todemodulate packets received from the antennas.

In some cases, the wireless device may include a single antenna 1125.However, in some cases the device may have more than one antenna 1125,which may be capable of concurrently transmitting or receiving multiplewireless transmissions.

The memory 1130 may include RAM and ROM. The memory 1130 may storecomputer-readable, computer-executable code 1135 including instructionsthat, when executed, cause the processor to perform various functionsdescribed herein. In some cases, the memory 1130 may contain, amongother things, a BIOS which may control basic hardware or softwareoperation such as the interaction with peripheral components or devices.

The processor 1140 may include an intelligent hardware device, (e.g., ageneral-purpose processor, a DSP, a CPU, a microcontroller, an ASIC, anFPGA, a programmable logic device, a discrete gate or transistor logiccomponent, a discrete hardware component, or any combination thereof).In some cases, the processor 1140 may be configured to operate a memoryarray using a memory controller. In other cases, a memory controller maybe integrated into the processor 1140. The processor 1140 may beconfigured to execute computer-readable instructions stored in a memory(e.g., the memory 1130) to cause the device 1105 to perform variousfunctions (e.g., functions or tasks supporting CHO deconfiguration andfailure handling in wireless communications).

The code 1135 may include instructions to implement aspects of thepresent disclosure, including instructions to support wirelesscommunications. The code 1135 may be stored in a non-transitorycomputer-readable medium such as system memory or other type of memory.In some cases, the code 1135 may not be directly executable by theprocessor 1140 but may cause a computer (e.g., when compiled andexecuted) to perform functions described herein.

FIG. 12 shows a block diagram 1200 of a device 1205 that supports CHOdeconfiguration and failure handling in wireless communications inaccordance with aspects of the present disclosure. The device 1205 maybe an example of aspects of a base station 105 as described herein. Thedevice 1205 may include a receiver 1210, a communications manager 1215,and a transmitter 1220. The device 1205 may also include a processor.Each of these components may be in communication with one another (e.g.,via one or more buses).

The receiver 1210 may receive information such as packets, user data, orcontrol information associated with various information channels (e.g.,control channels, data channels, and information related to CHOdeconfiguration and failure handling in wireless communications, etc.).Information may be passed on to other components of the device 1205. Thereceiver 1210 may be an example of aspects of the transceiver 1520described with reference to FIG. 15. The receiver 1210 may utilize asingle antenna or a set of antennas.

The communications manager 1215 may establish, by the source basestation, one or more conditional handover configurations with one ormore target base stations for a conditional handover of a UE from thesource base station to the respective target base station, where eachconditional handover configuration includes a conditional handover timeperiod for completing a random access procedure upon initiation of theconditional handover of the UE from the source base station to therespective target base station and transmit, to the UE, the one or moreconditional handover configurations that each indicate an associatedtarget base station, one or more measurement thresholds for initiatingthe handover of the UE from the source base station to the associatedtarget base station, and the conditional handover time period of theassociated target base station.

The communications manager 1215 may also establish, by the source basestation, one or more conditional handover configurations with one ormore target base stations for a conditional handover of a UE from thesource base station to the respective target base station, where eachconditional handover configuration includes a triggering measurementthreshold for initiating the conditional handover of the UE to anassociated target base station and a conditional handover timer valuefor completing the conditional handover of the UE to the associatedtarget base station, and transmit, to the UE, the one or moreconditional handover configurations that each indicate the associatedtarget base station, the triggering measurement threshold for initiatingthe conditional handover to the associated target base station and theconditional handover timer value for completing the conditional handoverof the UE to the associated target base station. The communicationsmanager 1215 may be an example of aspects of the communications manager1510 described herein.

The communications manager 1215, or its sub-components, may beimplemented in hardware, code (e.g., software or firmware) executed by aprocessor, or any combination thereof. If implemented in code executedby a processor, the functions of the communications manager 1215, or itssub-components may be executed by a general-purpose processor, a DSP, anapplication-specific integrated circuit (ASIC), a FPGA or otherprogrammable logic device, discrete gate or transistor logic, discretehardware components, or any combination thereof designed to perform thefunctions described in the present disclosure.

The communications manager 1215, or its sub-components, may bephysically located at various positions, including being distributedsuch that portions of functions are implemented at different physicallocations by one or more physical components. In some examples, thecommunications manager 1215, or its sub-components, may be a separateand distinct component in accordance with various aspects of the presentdisclosure. In some examples, the communications manager 1215, or itssub-components, may be combined with one or more other hardwarecomponents, including but not limited to an input/output (I/O)component, a transceiver, a network server, another computing device,one or more other components described in the present disclosure, or acombination thereof in accordance with various aspects of the presentdisclosure.

The transmitter 1220 may transmit signals generated by other componentsof the device 1205. In some examples, the transmitter 1220 may becollocated with a receiver 1210 in a transceiver module. For example,the transmitter 1220 may be an example of aspects of the transceiver1520 described with reference to FIG. 15. The transmitter 1220 mayutilize a single antenna or a set of antennas.

FIG. 13 shows a block diagram 1300 of a device 1305 that supports CHOdeconfiguration and failure handling in wireless communications inaccordance with aspects of the present disclosure. The device 1305 maybe an example of aspects of a device 1205, or a base station 105 asdescribed herein. The device 1305 may include a receiver 1310, acommunications manager 1315, and a transmitter 1330. The device 1305 mayalso include a processor. Each of these components may be incommunication with one another (e.g., via one or more buses).

The receiver 1310 may receive information such as packets, user data, orcontrol information associated with various information channels (e.g.,control channels, data channels, and information related to CHOdeconfiguration and failure handling in wireless communications, etc.).Information may be passed on to other components of the device 1305. Thereceiver 1310 may be an example of aspects of the transceiver 1520described with reference to FIG. 15. The receiver 1310 may utilize asingle antenna or a set of antennas.

The communications manager 1315 may be an example of aspects of thecommunications manager 1215 as described herein. The communicationsmanager 1315 may include a handover configuration manager 1320 and an UEhandover manager 1325. The communications manager 1315 may be an exampleof aspects of the communications manager 1510 described herein.

The handover configuration manager 1320 may establish, by the sourcebase station, one or more conditional handover configurations with oneor more target base stations for a conditional handover of a UE from thesource base station to the respective target base station, where eachconditional handover configuration includes a conditional handover timeperiod for completing a random access procedure upon initiation of theconditional handover of the UE from the source base station to therespective target base station.

The UE handover manager 1325 may transmit, to the UE, the one or moreconditional handover configurations that each indicate an associatedtarget base station, one or more measurement thresholds for initiatingthe handover of the UE from the source base station to the associatedtarget base station, and the conditional handover time period of theassociated target base station.

The handover configuration manager 1320 may establish, by the sourcebase station, one or more conditional handover configurations with oneor more target base stations for a conditional handover of a UE from thesource base station to the respective target base station, where eachconditional handover configuration includes a triggering measurementthreshold for initiating the conditional handover of the UE to anassociated target base station and a conditional handover timer valuefor completing the conditional handover of the UE to the associatedtarget base station.

The UE handover manager 1325 may transmit, to the UE, the one or moreconditional handover configurations that each indicate the associatedtarget base station, the triggering measurement threshold for initiatingthe conditional handover to the associated target base station, and theconditional handover timer value for completing the conditional handoverof the UE to the associated target base station.

The transmitter 1330 may transmit signals generated by other componentsof the device 1305. In some examples, the transmitter 1330 may becollocated with a receiver 1310 in a transceiver module. For example,the transmitter 1330 may be an example of aspects of the transceiver1520 described with reference to FIG. 15. The transmitter 1330 mayutilize a single antenna or a set of antennas.

FIG. 14 shows a block diagram 1400 of a communications manager 1405 thatsupports CHO deconfiguration and failure handling in wirelesscommunications in accordance with aspects of the present disclosure. Thecommunications manager 1405 may be an example of aspects of acommunications manager 1215, a communications manager 1315, or acommunications manager 1510 described herein. The communications manager1405 may include a handover configuration manager 1410, an UE handovermanager 1415, a timer manager 1420, and a measurement manager 1425. Eachof these modules may communicate, directly or indirectly, with oneanother (e.g., via one or more buses).

The handover configuration manager 1410 may establish, by the sourcebase station, one or more conditional handover configurations with oneor more target base stations for a conditional handover of a UE from thesource base station to the respective target base station, where eachconditional handover configuration includes a conditional handover timeperiod for completing a random access procedure upon initiation of theconditional handover of the UE from the source base station to therespective target base station.

In some examples, the handover configuration manager 1410 may establish,by the source base station, one or more conditional handoverconfigurations with one or more target base stations for a conditionalhandover of a UE from the source base station to the respective targetbase station, where each conditional handover configuration includes atriggering measurement threshold for initiating the conditional handoverof the UE to an associated target base station and a deconfigurationmeasurement threshold for deconfiguring the conditional handoverconfiguration of the associated target base station.

In some examples, the handover configuration manager 1410 may releasethe first conditional handover configuration of the first target basestation responsive to the measurement report. In some examples, thehandover configuration manager 1410 may delete one or more of a radioresource control configuration, the first deconfiguration measurementthreshold, a first triggering measurement threshold, or one or moretimers associated with the first target base station, that are includedin the first conditional handover configuration. In some examples, thehandover configuration manager 1410 may provide an indication to thefirst target base station that the first conditional handoverconfiguration is released.

In some cases, the deconfiguration measurement threshold is a channelquality threshold associated with each respective target base station,and where the conditional handover configuration of a first target basestation is released responsive to a channel quality measurement of thefirst target base station being below the channel quality threshold ofthe first target base station. In some cases, the deconfigurationmeasurement threshold includes a first threshold value associated withthe source base station and a second threshold value for each respectivetarget base station, and where the conditional handover configuration ofa first target base station is released responsive to a first channelquality measurement of the source base station exceeding the firstthreshold and a second channel quality measurement of the first targetbase station being below the second threshold value of the first targetbase station. In some cases, the deconfiguration measurement thresholdis a difference threshold, and where the conditional handoverconfiguration associated with a first target base station is releasedresponsive to a difference between channel quality measurements of thesource base station and the first target base station exceeding thedifference threshold.

The UE handover manager 1415 may transmit, to the UE, the one or moreconditional handover configurations that each indicate an associatedtarget base station, one or more measurement thresholds for initiatingthe handover of the UE from the source base station to the associatedtarget base station, and the conditional handover time period of theassociated target base station.

In some examples, the UE handover manager 1415 may transmit, to the UE,the one or more conditional handover configurations that each indicatethe associated target base station, the triggering measurement thresholdfor initiating the conditional handover to the associated target basestation, and the deconfiguration measurement threshold for deconfiguringthe conditional handover configuration of the associated target basestation. In some cases, the UE autonomously deconfigures the firstconditional handover configuration of the first target base stationbased on the expiration of the first validity time period.

The timer manager 1420 may manage one or more times associated with CHO.In some cases the conditional handover time period is determined basedon one or more of an estimate of movement of the UE relative to eachrespective target base station, a traffic load of the source basestation or each respective target base station, channel qualitymeasurements for each respective target base station provided by the UE,or any combinations thereof.

The measurement manager 1425 may receive, from the UE, a measurementreport that indicates that a first deconfiguration measurement thresholdfor deconfiguring a first conditional handover configuration of a firsttarget base station is satisfied.

FIG. 15 shows a diagram of a system 1500 including a device 1505 thatsupports CHO deconfiguration and failure handling in wirelesscommunications in accordance with aspects of the present disclosure. Thedevice 1505 may be an example of or include the components of device1205, device 1305, or a base station 105 as described herein. The device1505 may include components for bi-directional voice and datacommunications including components for transmitting and receivingcommunications, including a communications manager 1510, a networkcommunications manager 1515, a transceiver 1520, an antenna 1525, memory1530, a processor 1540, and an inter-station communications manager1545. These components may be in electronic communication via one ormore buses (e.g., bus 1550).

The communications manager 1510 may establish, by the source basestation, one or more conditional handover configurations with one ormore target base stations for a conditional handover of a UE from thesource base station to the respective target base station, where eachconditional handover configuration includes a conditional handover timeperiod for completing a random access procedure upon initiation of theconditional handover of the UE from the source base station to therespective target base station and transmit, to the UE, the one or moreconditional handover configurations that each indicate an associatedtarget base station, one or more measurement thresholds for initiatingthe handover of the UE from the source base station to the associatedtarget base station, and the conditional handover time period of theassociated target base station.

The communications manager 1510 may also establish, by the source basestation, one or more conditional handover configurations with one ormore target base stations for a conditional handover of a UE from thesource base station to the respective target base station, where eachconditional handover configuration includes a triggering measurementthreshold for initiating the conditional handover of the UE to anassociated target base station and a conditional handover timer valuefor completing the conditional handover of the UE to the associatedtarget base station, and transmit, to the UE, the one or moreconditional handover configurations that each indicate the associatedtarget base station, the triggering measurement threshold for initiatingthe conditional handover to the associated target base station, and theconditional handover timer value for completing the conditional handoverof the UE to the associated target base station.

The network communications manager 1515 may manage communications withthe core network (e.g., via one or more wired backhaul links). Forexample, the network communications manager 1515 may manage the transferof data communications for client devices, such as one or more UEs 115.

The transceiver 1520 may communicate bi-directionally, via one or moreantennas, wired, or wireless links as described above. For example, thetransceiver 1520 may represent a wireless transceiver and maycommunicate bi-directionally with another wireless transceiver. Thetransceiver 1520 may also include a modem to modulate the packets andprovide the modulated packets to the antennas for transmission, and todemodulate packets received from the antennas.

In some cases, the wireless device may include a single antenna 1525.However, in some cases the device may have more than one antenna 1525,which may be capable of concurrently transmitting or receiving multiplewireless transmissions.

The memory 1530 may include RAM, ROM, or a combination thereof. Thememory 1530 may store computer-readable code 1535 including instructionsthat, when executed by a processor (e.g., the processor 1540) cause thedevice to perform various functions described herein. In some cases, thememory 1530 may contain, among other things, a BIOS which may controlbasic hardware or software operation such as the interaction withperipheral components or devices.

The processor 1540 may include an intelligent hardware device, (e.g., ageneral-purpose processor, a DSP, a CPU, a microcontroller, an ASIC, anFPGA, a programmable logic device, a discrete gate or transistor logiccomponent, a discrete hardware component, or any combination thereof).In some cases, the processor 1540 may be configured to operate a memoryarray using a memory controller. In some cases, a memory controller maybe integrated into processor 1540. The processor 1540 may be configuredto execute computer-readable instructions stored in a memory (e.g., thememory 1530) to cause the device 1505 to perform various functions(e.g., functions or tasks supporting CHO deconfiguration and failurehandling in wireless communications).

The inter-station communications manager 1545 may manage communicationswith other base station 105, and may include a controller or schedulerfor controlling communications with UEs 115 in cooperation with otherbase stations 105. For example, the inter-station communications manager1545 may coordinate scheduling for transmissions to UEs 115 for variousinterference mitigation techniques such as beamforming or jointtransmission. In some examples, the inter-station communications manager1545 may provide an X2 interface within an LTE/LTE-A wirelesscommunication network technology to provide communication between basestations 105.

The code 1535 may include instructions to implement aspects of thepresent disclosure, including instructions to support wirelesscommunications. The code 1535 may be stored in a non-transitorycomputer-readable medium such as system memory or other type of memory.In some cases, the code 1535 may not be directly executable by theprocessor 1540 but may cause a computer (e.g., when compiled andexecuted) to perform functions described herein.

FIG. 16 shows a flowchart illustrating a method 1600 that supports CHOdeconfiguration and failure handling in wireless communications inaccordance with aspects of the present disclosure. The operations ofmethod 1600 may be implemented by a UE 115 or its components asdescribed herein. For example, the operations of method 1600 may beperformed by a communications manager as described with reference toFIGS. 8 through 11. In some examples, a UE may execute a set ofinstructions to control the functional elements of the UE to perform thefunctions described below. Additionally or alternatively, a UE mayperform aspects of the functions described below using special-purposehardware.

At 1605, the UE may receive, from a source base station, a conditionalhandover configuration that indicates one or more target base stations,one or more measurement thresholds for initiating a handover from thesource base station to the one or more target base stations, and one ormore timers associated with the handover to the one or more target basestations. The operations of 1605 may be performed according to themethods described herein. In some examples, aspects of the operations of1605 may be performed by a handover configuration manager as describedwith reference to FIGS. 8 through 11.

At 1610, the UE may determine, based on the conditional handoverconfiguration, that a first measurement threshold for initiating thehandover to a first target base station is satisfied. The operations of1610 may be performed according to the methods described herein. In someexamples, aspects of the operations of 1610 may be performed by ameasurement manager as described with reference to FIGS. 8 through 11.

At 1615, the UE may transmit, based on the conditional handoverconfiguration, a first random access request to the first target basestation to initiate a first random access procedure for the handover tothe first target base station. The operations of 1615 may be performedaccording to the methods described herein. In some examples, aspects ofthe operations of 1615 may be performed by a random access manager asdescribed with reference to FIGS. 8 through 11.

At 1620, the UE may start a first conditional handover timer forcompleting the first random access procedure responsive to thetransmitting the first random access request. The operations of 1620 maybe performed according to the methods described herein. In someexamples, aspects of the operations of 1620 may be performed by aconditional handover timer as described with reference to FIGS. 8through 11.

At 1625, the UE may determine a first conditional handover failureresponsive to the first conditional handover timer expiring prior tocompleting the first random access procedure. The operations of 1625 maybe performed according to the methods described herein. In someexamples, aspects of the operations of 1625 may be performed by ahandover configuration manager as described with reference to FIGS. 8through 11.

FIG. 17 shows a flowchart illustrating a method 1700 that supports CHOdeconfiguration and failure handling in wireless communications inaccordance with aspects of the present disclosure. The operations ofmethod 1700 may be implemented by a UE 115 or its components asdescribed herein. For example, the operations of method 1700 may beperformed by a communications manager as described with reference toFIGS. 8 through 11. In some examples, a UE may execute a set ofinstructions to control the functional elements of the UE to perform thefunctions described below. Additionally or alternatively, a UE mayperform aspects of the functions described below using special-purposehardware.

At 1705, the UE may receive, from a source base station, a conditionalhandover configuration that indicates one or more target base stations,one or more measurement thresholds for initiating a handover from thesource base station to the one or more target base stations, and one ormore timers associated with the handover to the one or more target basestations. The operations of 1705 may be performed according to themethods described herein. In some examples, aspects of the operations of1705 may be performed by a handover configuration manager as describedwith reference to FIGS. 8 through 11.

At 1710, the UE may determine, based on the conditional handoverconfiguration, that a first measurement threshold for initiating thehandover to a first target base station is satisfied. The operations of1710 may be performed according to the methods described herein. In someexamples, aspects of the operations of 1710 may be performed by ameasurement manager as described with reference to FIGS. 8 through 11.

At 1715, the UE may transmit, based on the conditional handoverconfiguration, a first random access request to the first target basestation to initiate a first random access procedure for the handover tothe first target base station. The operations of 1715 may be performedaccording to the methods described herein. In some examples, aspects ofthe operations of 1715 may be performed by a random access manager asdescribed with reference to FIGS. 8 through 11.

At 1720, the UE may start a first conditional handover timer forcompleting the first random access procedure responsive to thetransmitting the first random access request. The operations of 1720 maybe performed according to the methods described herein. In someexamples, aspects of the operations of 1720 may be performed by aconditional handover timer as described with reference to FIGS. 8through 11.

At 1725, the UE may determine a first conditional handover failureresponsive to the first conditional handover timer expiring prior tocompleting the first random access procedure. The operations of 1725 maybe performed according to the methods described herein. In someexamples, aspects of the operations of 1725 may be performed by ahandover configuration manager as described with reference to FIGS. 8through 11.

At 1730, the UE may determine, responsive to the first conditionalhandover timer expiring, that a second measurement threshold forinitiating a handover to a second target base station is satisfied. Theoperations of 1730 may be performed according to the methods describedherein. In some examples, aspects of the operations of 1730 may beperformed by a measurement manager as described with reference to FIGS.8 through 11.

At 1735, the UE may transmit, based on the conditional handoverconfiguration, a second random access request to the second target basestation to initiate a second random access procedure for the handover tothe second target base station. The operations of 1735 may be performedaccording to the methods described herein. In some examples, aspects ofthe operations of 1735 may be performed by a random access manager asdescribed with reference to FIGS. 8 through 11.

At 1740, the UE may start a second conditional handover timer forcompleting the second random access procedure. The operations of 1740may be performed according to the methods described herein. In someexamples, aspects of the operations of 1740 may be performed by aconditional handover timer as described with reference to FIGS. 8through 11.

At 1745, the UE may repeat the determining, transmitting, and startingfor any other target base stations configured for conditional handoverupon further conditional handover failures. The operations of 1745 maybe performed according to the methods described herein. In someexamples, aspects of the operations of 1745 may be performed by ahandover configuration manager as described with reference to FIGS. 8through 11.

At 1750, the UE may initiate a connection re-establishment procedureupon determining that no other target base stations are configured forconditional handover. The operations of 1750 may be performed accordingto the methods described herein. In some examples, aspects of theoperations of 1750 may be performed by a RRC connection establishmentcomponent as described with reference to FIGS. 8 through 11.

FIG. 18 shows a flowchart illustrating a method 1800 that supports CHOdeconfiguration and failure handling in wireless communications inaccordance with aspects of the present disclosure. The operations ofmethod 1800 may be implemented by a UE 115 or its components asdescribed herein. For example, the operations of method 1800 may beperformed by a communications manager as described with reference toFIGS. 8 through 11. In some examples, a UE may execute a set ofinstructions to control the functional elements of the UE to perform thefunctions described below. Additionally or alternatively, a UE mayperform aspects of the functions described below using special-purposehardware.

At 1805, the UE may receive, from a source base station, a conditionalhandover configuration that indicates one or more conditional handoverconfigurations associated with one or more target base stations, whereeach of the one or more conditional handover configurations include atriggering measurement threshold for initiating a conditional handoverto an associated target base station and a deconfiguration measurementthreshold for deconfiguring the conditional handover configuration ofthe associated target base station. The operations of 1805 may beperformed according to the methods described herein. In some examples,aspects of the operations of 1805 may be performed by a handoverconfiguration manager as described with reference to FIGS. 8 through 11.

At 1810, the UE may determine, based on the conditional handoverconfiguration, that a first deconfiguration measurement threshold fordeconfiguring a first conditional handover configuration of a firsttarget base station is satisfied. The operations of 1810 may beperformed according to the methods described herein. In some examples,aspects of the operations of 1810 may be performed by a measurementmanager as described with reference to FIGS. 8 through 11.

At 1815, the UE may release the first conditional handover configurationof the first target base station. The operations of 1815 may beperformed according to the methods described herein. In some examples,aspects of the operations of 1815 may be performed by a handoverconfiguration manager as described with reference to FIGS. 8 through 11.

FIG. 19 shows a flowchart illustrating a method 1900 that supports CHOdeconfiguration and failure handling in wireless communications inaccordance with aspects of the present disclosure. The operations ofmethod 1900 may be implemented by a UE 115 or its components asdescribed herein. For example, the operations of method 1900 may beperformed by a communications manager as described with reference toFIGS. 8 through 11. In some examples, a UE may execute a set ofinstructions to control the functional elements of the UE to perform thefunctions described below. Additionally or alternatively, a UE mayperform aspects of the functions described below using special-purposehardware.

At 1905, the UE may receive, from a source base station, a conditionalhandover configuration that indicates one or more conditional handoverconfigurations associated with one or more target base stations, whereeach of the one or more conditional handover configurations include atriggering measurement threshold for initiating a conditional handoverto an associated target base station and a deconfiguration measurementthreshold for deconfiguring the conditional handover configuration ofthe associated target base station. The operations of 1905 may beperformed according to the methods described herein. In some examples,aspects of the operations of 1905 may be performed by a handoverconfiguration manager as described with reference to FIGS. 8 through 11.

At 1910, the UE may determine, based on the conditional handoverconfiguration, that a first deconfiguration measurement threshold fordeconfiguring a first conditional handover configuration of a firsttarget base station is satisfied. The operations of 1910 may beperformed according to the methods described herein. In some examples,aspects of the operations of 1910 may be performed by a measurementmanager as described with reference to FIGS. 8 through 11.

At 1915, the UE may release the first conditional handover configurationof the first target base station. The operations of 1915 may beperformed according to the methods described herein. In some examples,aspects of the operations of 1915 may be performed by a handoverconfiguration manager as described with reference to FIGS. 8 through 11.

At 1920, the UE may determine, based on the conditional handoverconfiguration, that a second triggering measurement threshold forinitiating a handover to a second target base station is satisfied. Theoperations of 1920 may be performed according to the methods describedherein. In some examples, aspects of the operations of 1920 may beperformed by a measurement manager as described with reference to FIGS.8 through 11.

At 1925, the UE may transmit, based on a second conditional handoverconfiguration of the second target base station, a random access requestto the second target base station to initiate a random access procedurefor the handover to the second target base station. The operations of1925 may be performed according to the methods described herein. In someexamples, aspects of the operations of 1925 may be performed by a randomaccess manager as described with reference to FIGS. 8 through 11.

FIG. 20 shows a flowchart illustrating a method 2000 that supports CHOdeconfiguration and failure handling in wireless communications inaccordance with aspects of the present disclosure. The operations ofmethod 2000 may be implemented by a UE 115 or its components asdescribed herein. For example, the operations of method 2000 may beperformed by a communications manager as described with reference toFIGS. 8 through 11. In some examples, a UE may execute a set ofinstructions to control the functional elements of the UE to perform thefunctions described below. Additionally or alternatively, a UE mayperform aspects of the functions described below using special-purposehardware.

At 2005, the UE may receive, from a source base station, a conditionalhandover configuration that indicates one or more conditional handoverconfigurations associated with one or more target base stations, whereeach of the one or more conditional handover configurations include atriggering measurement threshold for initiating a conditional handoverto an associated target base station and a deconfiguration measurementthreshold for deconfiguring the conditional handover configuration ofthe associated target base station. The operations of 2005 may beperformed according to the methods described herein. In some examples,aspects of the operations of 2005 may be performed by a handoverconfiguration manager as described with reference to FIGS. 8 through 11.

At 2010, the UE may determine, based on the conditional handoverconfiguration, that a first deconfiguration measurement threshold fordeconfiguring a first conditional handover configuration of a firsttarget base station is satisfied. The operations of 2010 may beperformed according to the methods described herein. In some examples,aspects of the operations of 2010 may be performed by a measurementmanager as described with reference to FIGS. 8 through 11.

At 2015, the UE may release the first conditional handover configurationof the first target base station. The operations of 2015 may beperformed according to the methods described herein. In some examples,aspects of the operations of 2015 may be performed by a handoverconfiguration manager as described with reference to FIGS. 8 through 11.

At 2020, the UE may transmit a measurement report to the source basestation that indicates the first conditional handover configuration ofthe first target base station is released. The operations of 2020 may beperformed according to the methods described herein. In some examples,aspects of the operations of 2020 may be performed by a measurementmanager as described with reference to FIGS. 8 through 11.

At 2025, the UE may the measurement report contains a deconfigurationindication for the first target base station. The operations of 2025 maybe performed according to the methods described herein. In someexamples, aspects of the operations of 2025 may be performed by ameasurement manager as described with reference to FIGS. 8 through 11.

FIG. 21 shows a flowchart illustrating a method 2100 that supports CHOdeconfiguration and failure handling in wireless communications inaccordance with aspects of the present disclosure. The operations ofmethod 2100 may be implemented by a base station 105 or its componentsas described herein. For example, the operations of method 2100 may beperformed by a communications manager as described with reference toFIGS. 12 through 15. In some examples, a base station may execute a setof instructions to control the functional elements of the base stationto perform the functions described below. Additionally or alternatively,a base station may perform aspects of the functions described belowusing special-purpose hardware.

At 2105, the base station may establish, by the source base station, oneor more conditional handover configurations with one or more target basestations for a conditional handover of a UE from the source base stationto the respective target base station, where each conditional handoverconfiguration includes a conditional handover time period for completinga random access procedure upon initiation of the conditional handover ofthe UE from the source base station to the respective target basestation. The operations of 2105 may be performed according to themethods described herein. In some examples, aspects of the operations of2105 may be performed by a handover configuration manager as describedwith reference to FIGS. 12 through 15.

At 2110, the base station may transmit, to the UE, the one or moreconditional handover configurations that each indicate an associatedtarget base station, one or more measurement thresholds for initiatingthe handover of the UE from the source base station to the associatedtarget base station, and the conditional handover time period of theassociated target base station. The operations of 2110 may be performedaccording to the methods described herein. In some examples, aspects ofthe operations of 2110 may be performed by an UE handover manager asdescribed with reference to FIGS. 12 through 15.

FIG. 22 shows a flowchart illustrating a method 2200 that supports CHOdeconfiguration and failure handling in wireless communications inaccordance with aspects of the present disclosure. The operations ofmethod 2200 may be implemented by a base station 105 or its componentsas described herein. For example, the operations of method 2200 may beperformed by a communications manager as described with reference toFIGS. 12 through 15. In some examples, a base station may execute a setof instructions to control the functional elements of the base stationto perform the functions described below. Additionally or alternatively,a base station may perform aspects of the functions described belowusing special-purpose hardware.

At 2205, the base station may establish, by the source base station, oneor more conditional handover configurations with one or more target basestations for a conditional handover of a UE from the source base stationto the respective target base station, where each conditional handoverconfiguration includes a triggering measurement threshold for initiatingthe conditional handover of the UE to an associated target base stationand a conditional handover timer value for completing the conditionalhandover of the UE to the associated target base station. The operationsof 2205 may be performed according to the methods described herein. Insome examples, aspects of the operations of 2205 may be performed by ahandover configuration manager as described with reference to FIGS. 12through 15.

At 2210, the base station may transmit, to the UE, the one or moreconditional handover configurations that each indicate the associatedtarget base station, the triggering measurement threshold for initiatingthe conditional handover to the associated target base station, and theconditional handover timer value for completing the conditional handoverof the UE to the associated target base station. The operations of 2210may be performed according to the methods described herein. In someexamples, aspects of the operations of 2210 may be performed by an UEhandover manager as described with reference to FIGS. 12 through 15.

It should be noted that the methods described herein describe possibleimplementations, and that the operations and the steps may be rearrangedor otherwise modified and that other implementations are possible.Further, aspects from two or more of the methods may be combined.

Embodiment 1

A method of wireless communication, at a UE, comprising: receiving, froma source base station, a conditional handover configuration thatindicates one or more target base stations, one or more measurementthresholds for initiating a handover from the source base station to theone or more target base stations, and one or more timers associated withthe handover to the one or more target base stations; determining, basedat least in part on the conditional handover configuration, that a firstmeasurement threshold for initiating the handover to a first target basestation is satisfied; transmitting, based at least in part on theconditional handover configuration, a first random access request to thefirst target base station to initiate a first random access procedurefor the handover to the first target base station; starting a firstconditional handover timer for completing the first random accessprocedure responsive to the transmitting the first random accessrequest; and determining a first conditional handover failure responsiveto the first conditional handover timer expiring prior to completing thefirst random access procedure.

Embodiment 2

The method of embodiment 1, wherein the one or more timers include atleast the first conditional handover timer for completing the firstrandom access procedure with the first target base station.

Embodiment 3

The method of any of embodiments 1 or 2, wherein the conditionalhandover configuration includes at least a first conditional handoverconfiguration for the first target base station and a second conditionalhandover configuration for a second target base station.

Embodiment 4

The method of any of embodiments 1 to 3, further comprising: initiating,responsive to receiving the conditional handover configuration, a firstvalidity timer and a second validity timer; and deleting the secondconditional handover configuration responsive to an expiration of thesecond validity timer.

Embodiment 5

The method of embodiment 4, further comprising: stopping the firstvalidity timer upon transmitting the first random access request to thefirst target base station.

Embodiment 6

The method of any of embodiments 1 to 5, further comprising:determining, responsive to the first conditional handover timerexpiring, that a second measurement threshold for initiating a handoverto a second target base station is satisfied; transmitting, based atleast in part on the conditional handover configuration, a second randomaccess request to the second target base station to initiate a secondrandom access procedure for the handover to the second target basestation; and starting a second conditional handover timer for completingthe second random access procedure.

Embodiment 7

The method of embodiment 6, further comprising: initiating a connectionre-establishment procedure upon determining that no other target basestations are configured for conditional handover.

Embodiment 8

The method of any of embodiments 6 to 7, wherein a first duration of thefirst conditional handover timer is different than a second duration ofthe second conditional handover timer.

Embodiment 9

The method of any of embodiments 6 to 8, further comprising: selecting,responsive to the first conditional handover timer expiring, the secondtarget base station from a plurality of available target base stationsbased at least in part on a channel quality measurement associated witheach of the plurality of available target base stations.

Embodiment 10

The method of any of embodiments 6 to 9, wherein the second target basestation is selected based at least in part on the second target basestation having a shorter remaining validity timer duration than other ofthe plurality of available target base stations.

Embodiment 11

The method of any of embodiments 1 to 10, further comprising: receiving,from the source base station, a deconfiguration message thatdeconfigures one or more conditional handover configurations; anddeconfiguring the one or more conditional handover configurations basedat least in part on the deconfiguration message.

Embodiment 12

The method of embodiment 11, wherein the deconfiguration message isreceived in radio resource control signaling from the source basestation.

Embodiment 13

The method of any of embodiments 11 to 12, further comprising: deletingone or more of a radio resource control configuration or a firstmeasurement and reporting configuration for conditional handover triggerprovided in a first conditional handover configuration; anddiscontinuing conditional handover measurements associated with theconditional handover configuration and evaluation of whether themeasurements meet conditional handover criteria.

Embodiment 14

An apparatus comprising at least one means for performing a method ofany of embodiments 1 to 13.

Embodiment 15

An apparatus for wireless communications comprising a processor; memoryin electronic communication with the processor; and instructions storedin the memory and executable by the processor to cause the apparatus toperform a method of any of embodiments 1 to 13.

Embodiment 16

A non-transitory computer-readable medium storing code for wirelesscommunications, the code comprising instructions executable by aprocessor to perform a method of any of embodiments 1 to 13.

Embodiment 17

A method of wireless communication, at a user equipment (UE),comprising: receiving, from a source base station, a conditionalhandover configuration that indicates one or more conditional handoverconfigurations associated with one or more target base stations, whereineach of the one or more conditional handover configurations include atriggering measurement threshold for initiating a conditional handoverto an associated target base station and a deconfiguration measurementthreshold for deconfiguring the conditional handover configuration ofthe associated target base station; determining, based at least in parton the conditional handover configuration, that a first deconfigurationmeasurement threshold for deconfiguring a first conditional handoverconfiguration of a first target base station is satisfied; and releasingthe first conditional handover configuration of the first target basestation.

Embodiment 18

The method of embodiment 17, further comprising: determining, based atleast in part on the conditional handover configuration, that a secondtriggering measurement threshold for initiating a handover to a secondtarget base station is satisfied; and transmitting, based at least inpart on a second conditional handover configuration of the second targetbase station, a random access request to the second target base stationto initiate a random access procedure for the handover to the secondtarget base station.

Embodiment 19

The method of any of embodiments 17 to 18, wherein the releasing thefirst conditional handover configuration comprises: deleting one or moreof a radio resource control configuration, a first measurement andreporting configuration for conditional handover trigger and conditionalhandover deconfiguration trigger, or one or more timers associated withthe first target base station, that are provided in the firstconditional handover configuration; and discontinuing conditionalhandover measurements associated with the first target base station andevaluating whether the measurements meet conditional handover criteriaor conditional handover deconfiguration criteria.

Embodiment 20

The method of any of embodiments 17 to 19, further comprising:transmitting a measurement report to the source base station thatindicates the first conditional handover configuration of the firsttarget base station is released.

Embodiment 21

The method of any of embodiments 17 to 20, further wherein themeasurement report contains a deconfiguration indication for the firsttarget base station.

Embodiment 22

The method of any of embodiments 17 to 21, wherein the firstdeconfiguration measurement threshold is a channel quality thresholdassociated with the first target base station, and wherein the firstconditional handover configuration is released responsive to a channelquality measurement of the first target base station being below thechannel quality threshold.

Embodiment 23

The method of any of embodiments 17 to 22, wherein the firstdeconfiguration measurement threshold comprises a first threshold valueassociated with the source base station and a second threshold valueassociated with the first target base station, and wherein the firstconditional handover configuration is released responsive to a firstchannel quality measurement of the source base station exceeding thefirst threshold and a second channel quality measurement of the firsttarget base station being below the second threshold value.

Embodiment 24

The method of any of embodiments 17 to 23, wherein the firstdeconfiguration measurement threshold is a difference threshold, andwherein the first conditional handover configuration is releasedresponsive to a difference between channel quality measurements of thesource base station and the first target base station exceeding thedifference threshold.

Embodiment 25

An apparatus comprising at least one means for performing a method ofany of embodiments 17 to 24.

Embodiment 26

An apparatus for wireless communications comprising a processor; memoryin electronic communication with the processor; and instructions storedin the memory and executable by the processor to cause the apparatus toperform a method of any of embodiments 17 to 24.

Embodiment 27

A non-transitory computer-readable medium storing code for wirelesscommunications, the code comprising instructions executable by aprocessor to perform a method of any of embodiments 17 to 24.

Embodiment 28

A method for wireless communication at a source base station,comprising: establishing, by the source base station, one or moreconditional handover configurations with one or more target basestations for a conditional handover of a user equipment (UE) from thesource base station to the respective target base station, wherein eachconditional handover configuration includes a validity time periodduring which the conditional handover configuration is valid and aconditional handover time period for completing a random accessprocedure upon initiation of the conditional handover of the UE from thesource base station to the respective target base station; andtransmitting, to the UE, the one or more conditional handoverconfigurations that each indicate an associated target base station, oneor more measurement thresholds for initiating the handover of the UEfrom the source base station to the associated target base station, andthe conditional handover time period of the associated target basestation.

Embodiment 29

The method of embodiment 28, further comprising: deconfiguring a firstconditional handover configuration of a first target base stationresponsive to an expiration of a first validity time period associatedwith the first target base station.

Embodiment 30

The method of any of embodiments 28 to 29, wherein the UE autonomouslydeconfigures the first conditional handover configuration of the firsttarget base station based on the expiration of the first validity timeperiod.

Embodiment 31

The method of any of embodiments 28 to 30, wherein each of the one ormore target base stations has a different value for one or more of thevalidity time period or the conditional handover time period.

Embodiment 32

The method of any of embodiments 28 to 31, wherein one or more of thevalidity time period or the conditional handover time period isdetermined based at least in part on one or more of an estimate ofmovement of the UE relative to each respective target base station, atraffic load of the source base station or each respective target basestation, channel quality measurements for each respective target basestation provided by the UE, or any combinations thereof.

Embodiment 33

An apparatus comprising at least one means for performing a method ofany of embodiments 28 to 32.

Embodiment 34

An apparatus for wireless communications comprising a processor; memoryin electronic communication with the processor; and instructions storedin the memory and executable by the processor to cause the apparatus toperform a method of any of embodiments 28 to 32.

Embodiment 35

A non-transitory computer-readable medium storing code for wirelesscommunications, the code comprising instructions executable by aprocessor to perform a method of any of embodiments 28 to 32.

Embodiment 36

A method for wireless communication at a source base station,comprising: establishing, by the source base station, one or moreconditional handover configurations with one or more target basestations for a conditional handover of a user equipment (UE) from thesource base station to the respective target base station, wherein eachconditional handover configuration includes a triggering measurementthreshold for initiating the conditional handover of the UE to anassociated target base station and a conditional handover timer valuefor completing the conditional handover of the UE to the associatedtarget base station; and transmitting, to the UE, the one or moreconditional handover configurations that each indicate the associatedtarget base station, the triggering measurement threshold for initiatingthe conditional handover to the associated target base station, and theconditional handover timer value for completing the conditional handoverof the UE to the associated target base station.

Embodiment 37

The method of embodiment 36, further comprising: determining todeconfigure at least one a first conditional handover configuration atthe UE; transmitting, responsive to the determining to deconfigure,deconfiguration information to the UE that indicates the UE is to deleteone or more of a radio resource control configuration or a firstmeasurement and reporting configuration for the first conditionalhandover configuration; receiving, from the UE, a measurement reportthat indicates that a first deconfiguration measurement threshold fordeconfiguring a first conditional handover configuration of a firsttarget base station is satisfied; and releasing the first conditionalhandover configuration of the first target base station responsive tothe measurement report.

Embodiment 38

The method of any of embodiments 36 to 37, wherein the releasing thefirst conditional handover configuration comprises: deleting one or moreof a radio resource control configuration, the first deconfigurationmeasurement threshold, a first triggering measurement threshold, or oneor more timers associated with the first target base station, that areincluded in the first conditional handover configuration.

Embodiment 39

The method of any of embodiments 36 to 38, wherein the releasing thefirst conditional handover configuration further comprises: providing anindication to the first target base station that the first conditionalhandover configuration is released.

Embodiment 40

The method of any of embodiments 36 to 39, wherein the deconfigurationmeasurement threshold is a channel quality threshold associated witheach respective target base station, and wherein the conditionalhandover configuration of a first target base station is releasedresponsive to a channel quality measurement of the first target basestation being below the channel quality threshold of the first targetbase station.

Embodiment 41

The method of any of embodiments 36 to 40, wherein the deconfigurationmeasurement threshold comprises a first threshold value associated withthe source base station and a second threshold value for each respectivetarget base station, and wherein the conditional handover configurationof a first target base station is released responsive to a first channelquality measurement of the source base station exceeding the firstthreshold and a second channel quality measurement of the first targetbase station being below the second threshold value of the first targetbase station.

Embodiment 42

The method of any of embodiments 36 to 41, wherein the deconfigurationmeasurement threshold is a difference threshold, and wherein theconditional handover configuration associated with a first target basestation is released responsive to a difference between channel qualitymeasurements of the source base station and the first target basestation exceeding the difference threshold.

Embodiment 43

An apparatus comprising at least one means for performing a method ofany of embodiments 36 to 42.

Embodiment 44

An apparatus for wireless communications comprising a processor; memoryin electronic communication with the processor; and instructions storedin the memory and executable by the processor to cause the apparatus toperform a method of any of embodiments 36 to 42.

Embodiment 45

A non-transitory computer-readable medium storing code for wirelesscommunications, the code comprising instructions executable by aprocessor to perform a method of any of embodiments 36 to 42.

Techniques described herein may be used for various wirelesscommunications systems such as code division multiple access (CDMA),time division multiple access (TDMA), frequency division multiple access(FDMA), orthogonal frequency division multiple access (OFDMA), singlecarrier frequency division multiple access (SC-FDMA), and other systems.A CDMA system may implement a radio technology such as CDMA2000,Universal Terrestrial Radio Access (UTRA), etc. CDMA2000 covers IS-2000,IS-95, and IS-856 standards. IS-2000 Releases may be commonly referredto as CDMA2000 1×, 1×, etc. IS-856 (TIA-856) is commonly referred to asCDMA2000 1×EV-DO, High Rate Packet Data (HRPD), etc. UTRA includesWideband CDMA (WCDMA) and other variants of CDMA. A TDMA system mayimplement a radio technology such as Global System for MobileCommunications (GSM).

An OFDMA system may implement a radio technology such as Ultra MobileBroadband (UMB), Evolved UTRA (E-UTRA), Institute of Electrical andElectronics Engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE802.20, Flash-OFDM, etc. UTRA and E-UTRA are part of Universal MobileTelecommunications System (UMTS). LTE, LTE-A, and LTE-A Pro are releasesof UMTS that use E-UTRA. UTRA, E-UTRA, UMTS, LTE, LTE-A, LTE-A Pro, NR,and GSM are described in documents from the organization named “3rdGeneration Partnership Project” (3GPP). CDMA2000 and UMB are describedin documents from an organization named “3rd Generation PartnershipProject 2” (3GPP2). The techniques described herein may be used for thesystems and radio technologies mentioned herein as well as other systemsand radio technologies. While aspects of an LTE, LTE-A, LTE-A Pro, or NRsystem may be described for purposes of example, and LTE, LTE-A, LTE-APro, or NR terminology may be used in much of the description, thetechniques described herein are applicable beyond LTE, LTE-A, LTE-A Pro,or NR applications.

A macro cell generally covers a relatively large geographic area (e.g.,several kilometers in radius) and may allow unrestricted access by UEswith service subscriptions with the network provider. A small cell maybe associated with a lower-powered base station, as compared with amacro cell, and a small cell may operate in the same or different (e.g.,licensed, unlicensed, etc.) frequency bands as macro cells. Small cellsmay include pico cells, femto cells, and micro cells according tovarious examples. A pico cell, for example, may cover a small geographicarea and may allow unrestricted access by UEs with service subscriptionswith the network provider. A femto cell may also cover a smallgeographic area (e.g., a home) and may provide restricted access by UEshaving an association with the femto cell (e.g., UEs in a closedsubscriber group (CSG), UEs for users in the home, and the like). An eNBfor a macro cell may be referred to as a macro eNB. An eNB for a smallcell may be referred to as a small cell eNB, a pico eNB, a femto eNB, ora home eNB. An eNB may support one or multiple (e.g., two, three, four,and the like) cells, and may also support communications using one ormultiple component carriers.

The wireless communications systems described herein may supportsynchronous or asynchronous operation. For synchronous operation, thebase stations may have similar frame timing, and transmissions fromdifferent base stations may be approximately aligned in time. Forasynchronous operation, the base stations may have different frametiming, and transmissions from different base stations may not bealigned in time. The techniques described herein may be used for eithersynchronous or asynchronous operations.

Information and signals described herein may be represented using any ofa variety of different technologies and techniques. For example, data,instructions, commands, information, signals, bits, symbols, and chipsthat may be referenced throughout the description may be represented byvoltages, currents, electromagnetic waves, magnetic fields or particles,optical fields or particles, or any combination thereof.

The various illustrative blocks and modules described in connection withthe disclosure herein may be implemented or performed with ageneral-purpose processor, a DSP, an ASIC, an FPGA, or otherprogrammable logic device, discrete gate or transistor logic, discretehardware components, or any combination thereof designed to perform thefunctions described herein. A general-purpose processor may be amicroprocessor, but in the alternative, the processor may be anyconventional processor, controller, microcontroller, or state machine. Aprocessor may also be implemented as a combination of computing devices(e.g., a combination of a DSP and a microprocessor, multiplemicroprocessors, one or more microprocessors in conjunction with a DSPcore, or any other such configuration).

The functions described herein may be implemented in hardware, softwareexecuted by a processor, firmware, or any combination thereof. Ifimplemented in software executed by a processor, the functions may bestored on or transmitted over as one or more instructions or code on acomputer-readable medium. Other examples and implementations are withinthe scope of the disclosure and appended claims. For example, due to thenature of software, functions described herein can be implemented usingsoftware executed by a processor, hardware, firmware, hardwiring, orcombinations of any of these. Features implementing functions may alsobe physically located at various positions, including being distributedsuch that portions of functions are implemented at different physicallocations.

Computer-readable media includes both non-transitory computer storagemedia and communication media including any medium that facilitatestransfer of a computer program from one place to another. Anon-transitory storage medium may be any available medium that can beaccessed by a general purpose or special purpose computer. By way ofexample, and not limitation, non-transitory computer-readable media mayinclude random-access memory (RAM), read-only memory (ROM), electricallyerasable programmable ROM (EEPROM), flash memory, compact disk (CD) ROMor other optical disk storage, magnetic disk storage or other magneticstorage devices, or any other non-transitory medium that can be used tocarry or store desired program code means in the form of instructions ordata structures and that can be accessed by a general-purpose orspecial-purpose computer, or a general-purpose or special-purposeprocessor. Also, any connection is properly termed a computer-readablemedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio, and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition of medium.Disk and disc, as used herein, include CD, laser disc, optical disc,digital versatile disc (DVD), floppy disk and Blu-ray disc where disksusually reproduce data magnetically, while discs reproduce dataoptically with lasers. Combinations of the above are also includedwithin the scope of computer-readable media.

As used herein, including in the claims, “or” as used in a list of items(e.g., a list of items prefaced by a phrase such as “at least one of” or“one or more of”) indicates an inclusive list such that, for example, alist of at least one of A, B, or C means A or B or C or AB or AC or BCor ABC (i.e., A and B and C). Also, as used herein, the phrase “basedon” shall not be construed as a reference to a closed set of conditions.For example, an exemplary step that is described as “based on conditionA” may be based on both a condition A and a condition B withoutdeparting from the scope of the present disclosure. In other words, asused herein, the phrase “based on” shall be construed in the same manneras the phrase “based at least in part on.”

In the appended figures, similar components or features may have thesame reference label. Further, various components of the same type maybe distinguished by following the reference label by a dash and a secondlabel that distinguishes among the similar components. If just the firstreference label is used in the specification, the description isapplicable to any one of the similar components having the same firstreference label irrespective of the second reference label, or othersubsequent reference label.

The description set forth herein, in connection with the appendeddrawings, describes example configurations and does not represent allthe examples that may be implemented or that are within the scope of theclaims. The term “exemplary” used herein means “serving as an example,instance, or illustration,” and not “preferred” or “advantageous overother examples.” The detailed description includes specific details forthe purpose of providing an understanding of the described techniques.These techniques, however, may be practiced without these specificdetails. In some instances, well-known structures and devices are shownin block diagram form in order to avoid obscuring the concepts of thedescribed examples.

The description herein is provided to enable a person skilled in the artto make or use the disclosure. Various modifications to the disclosurewill be readily apparent to those skilled in the art, and the genericprinciples defined herein may be applied to other variations withoutdeparting from the scope of the disclosure. Thus, the disclosure is notlimited to the examples and designs described herein, but is to beaccorded the broadest scope consistent with the principles and novelfeatures disclosed herein.

What is claimed is:
 1. A method for wireless communication at a userequipment (UE), comprising: receiving, from a source base station, aconditional handover configuration that indicates one or more targetbase stations, one or more measurement thresholds for initiating ahandover from the source base station to the one or more target basestations, and one or more timers associated with the handover to the oneor more target base stations; determining, based at least in part on theconditional handover configuration, that a first measurement thresholdfor initiating the handover to a first target base station is satisfied;transmitting, based at least in part on the conditional handoverconfiguration, a first random access request to the first target basestation to initiate a first random access procedure for the handover tothe first target base station; starting a first conditional handovertimer for completing the first random access procedure responsive to thetransmitting the first random access request; and determining a firstconditional handover failure responsive to the first conditionalhandover timer expiring prior to completing the first random accessprocedure.
 2. The method of claim 1, wherein the one or more timersinclude at least the first conditional handover timer for completing thefirst random access procedure with the first target base station.
 3. Themethod of claim 1, wherein the conditional handover configurationincludes at least a first conditional handover configuration for thefirst target base station and a second conditional handoverconfiguration for a second target base station.
 4. The method of claim1, further comprising transmitting, responsive to the first conditionalhandover timer expiring, a second random access request to a secondtarget base station to initiate a second random access procedure for thehandover to the second target base station; and starting a secondconditional handover timer for completing the second random accessprocedure.
 5. The method of claim 4, further comprising: initiating aconnection re-establishment procedure upon determining that no othertarget base stations are configured for conditional handover.
 6. Themethod of claim 4, wherein a first duration of the first conditionalhandover timer is different than a second duration of the secondconditional handover timer.
 7. The method of claim 4, furthercomprising: selecting, responsive to the first conditional handovertimer expiring, the second target base station from a plurality ofavailable target base stations based at least in part on a channelquality measurement associated with each of the plurality of availabletarget base stations.
 8. The method of claim 1, further comprisinginitiating, responsive to the first conditional handover timer expiring,a connection re-establishment procedure.
 9. The method of claim 1,further comprising: receiving, from the source base station, adeconfiguration message that deconfigures one or more conditionalhandover configurations; and deconfiguring the one or more conditionalhandover configurations based at least in part on the deconfigurationmessage.
 10. The method of claim 9, wherein the deconfiguration messageis received in radio resource control signaling from the source basestation.
 11. The method of claim 9, further comprising: deleting one ormore of a radio resource control configuration or a first measurementand reporting configuration for conditional handover trigger provided ina first conditional handover configuration; and discontinuingconditional handover measurements associated with the conditionalhandover configuration and evaluation of whether the conditionalhandover measurements meet conditional handover criteria.
 12. Anapparatus for wireless communication at a user equipment (UE),comprising: a processor, memory in electronic communication with theprocessor; and instructions stored in the memory and executable by theprocessor to cause the apparatus to: receive, from a source basestation, a conditional handover configuration that indicates one or moretarget base stations, one or more measurement thresholds for initiatinga handover from the source base station to the one or more target basestations, and one or more timers associated with the handover to the oneor more target base stations; determine, based at least in part on theconditional handover configuration, that a first measurement thresholdfor initiating the handover to a first target base station is satisfied;transmit, based at least in part on the conditional handoverconfiguration, a first random access request to the first target basestation to initiate a first random access procedure for the handover tothe first target base station; start a first conditional handover timerfor completing the first random access procedure responsive to thetransmitting the first random access request; and determine a firstconditional handover failure responsive to the first conditionalhandover timer expiring prior to completing the first random accessprocedure.
 13. The apparatus of claim 12, wherein the one or more timersinclude at least the first conditional handover timer for completing thefirst random access procedure with the first target base station. 14.The apparatus of claim 12, wherein the instructions are furtherexecutable by the processor to cause the apparatus to: transmit,responsive to the first conditional handover timer expiring a secondrandom access request to a second target base station to initiate asecond random access procedure for the handover to the second targetbase station; and start a second conditional handover timer forcompleting the second random access procedure.
 15. The apparatus ofclaim 12, wherein the instructions are further executable by theprocessor to cause the apparatus to: initiate, responsive to the firstconditional handover timer expiring, a connection re-establishmentprocedure.
 16. The apparatus of claim 12, wherein the instructions arefurther executable by the processor to cause the apparatus to: receive,from the source base station, a deconfiguration message thatdeconfigures one or more conditional handover configurations; anddeconfigure the one or more conditional handover configurations based atleast in part on the deconfiguration message.
 17. The apparatus of claim16, wherein the deconfiguration message is received in radio resourcecontrol signaling from the source base station, and wherein theinstructions are further executable by the processor to cause theapparatus to: delete one or more of a radio resource controlconfiguration or a first measurement and reporting configuration forconditional handover trigger provided in a first conditional handoverconfiguration; and discontinue conditional handover measurementsassociated with the conditional handover configuration and evaluation ofwhether the conditional handover measurements meet conditional handovercriteria.
 18. The apparatus of claim 16, wherein the deconfigurationmessage is received in radio resource control signaling from the sourcebase station.
 19. The apparatus of claim 12, wherein the conditionalhandover configuration includes at least a first conditional handoverconfiguration for the first target base station and a second conditionalhandover configuration for a second target base station.
 20. Theapparatus of claim 14, wherein the instructions are further executableby the processor to cause the apparatus to: initiate a connectionre-establishment procedure upon determining that no other target basestations are configured for conditional handover.
 21. The apparatus ofclaim 14, wherein a first duration of the first conditional handovertimer is different than a second duration of the second conditionalhandover timer.
 22. The apparatus of claim 14, wherein the instructionsare further executable by the processor to cause the apparatus to:select, responsive to the first conditional handover timer expiring, thesecond target base station from a plurality of available target basestations based at least in part on a channel quality measurementassociated with each of the plurality of available target base stations.23. An apparatus for wireless communication at a user equipment (UE),comprising: means for receiving, from a source base station, aconditional handover configuration that indicates one or more targetbase stations, one or more measurement thresholds for initiating ahandover from the source base station to the one or more target basestations, and one or more timers associated with the handover to the oneor more target base stations; means for determining, based at least inpart on the conditional handover configuration, that a first measurementthreshold for initiating the handover to a first target base station issatisfied; means for transmitting, based at least in part on theconditional handover configuration, a first random access request to thefirst target base station to initiate a first random access procedurefor the handover to the first target base station; means for starting afirst conditional handover timer for completing the first random accessprocedure responsive to the transmitting the first random accessrequest; and means for determining a first conditional handover failureresponsive to the first conditional handover timer expiring prior tocompleting the first random access procedure.
 24. The apparatus of claim23, wherein the one or more timers include at least the firstconditional handover timer for completing the first random accessprocedure with the first target base station.
 25. The apparatus of claim23, further comprising: means for transmitting, responsive to the firstconditional handover timer expiring, a second random access request to asecond target base station to initiate a second random access procedurefor the handover to the second target base station; and means forstarting a second conditional handover timer for completing the secondrandom access procedure.
 26. The apparatus of claim 23, furthercomprising: means for initiating a connection re-establishment procedureupon determining that no other target base stations are configured forconditional handover.
 27. The apparatus of claim 23, further comprising:means for receiving, from the source base station, a deconfigurationmessage that deconfigures one or more conditional handoverconfigurations; and means for deconfiguring the one or more conditionalhandover configurations based at least in part on the deconfigurationmessage.
 28. The apparatus of claim 27, further comprising: means fordeleting one or more of a radio resource control configuration or afirst measurement and reporting configuration for conditional handovertrigger provided in a first conditional handover configuration; andmeans for discontinuing conditional handover measurements associatedwith the conditional handover configuration and evaluation of whetherthe conditional handover measurements meet conditional handovercriteria.
 29. A non-transitory computer-readable medium storing code forwireless communication at a user equipment (UE), the code comprisinginstructions executable by a processor to: receive, from a source basestation, a conditional handover configuration that indicates one or moretarget base stations, one or more measurement thresholds for initiatinga handover from the source base station to the one or more target basestations, and one or more timers associated with the handover to the oneor more target base stations; determine, based at least in part on theconditional handover configuration, that a first measurement thresholdfor initiating the handover to a first target base station is satisfied;transmit, based at least in part on the conditional handoverconfiguration, a first random access request to the first target basestation to initiate a first random access procedure for the handover tothe first target base station; start a first conditional handover timerfor completing the first random access procedure responsive to thetransmitting the first random access request; and determine a firstconditional handover failure responsive to the first conditionalhandover timer expiring prior to completing the first random accessprocedure.